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• Feedback on meeting of the Linux User Group of Mauritius

  Once upon a time in a country far far away... Okay, actually it's not that bad but it has been a while since the last meeting of the Linux User Group of Mauritius (LUGM). There have been plans in the past but it never really happened. Finally, Selven took the opportunity and organised a new meetup with low administrative overhead, proper scheduling on alternative dates and a small attendee's survey on the preferred option. All the pre-work was nicely executed. First, I wasn't sure whether it would be possible to attend. Luckily I got some additional information, like children should come, too, and I was sold to this community gathering. According to other long-term members of the LUGM it was the first time 'ever' that a gathering was organised outside of Quatre Bornes, and I have to admit it was great! LUGM - user group meeting on the 15.06.2013 in L'Escalier Quick overview of Linux & the LUGM With a little bit of delay the LUGM meeting officially started with a quick overview and introduction to Linux presented by Avinash. During the session he told the audience that there had been quite some activity over the island some years ago but unfortunately it had been quiet during recent times. Of course, we also spoke about the acknowledged world dominance of Linux - thanks to Android - and the interesting possibilities for countries like Mauritius. It is known that a couple of public institutions have there back-end infrastructure running on Red Hat Linux systems but the presence on the desktop is still very low. Users are simply hanging on to Windows XP and older versions of Microsoft Office. Following the introduction of the LUGM Ajay joined into the session and it quickly changed into a panel discussion with lots of interesting questions and answers, sharing of first-hand experience either on the job or in private use of Linux, and a couple of ideas about how the LUGM could promote Linux a bit more in Mauritius. It was great to get an insight into other attendee's opinion and activities. Especially taking into consideration that I'm already using Linux since around 1996/97. Frankly speaking, I bought a SuSE 4.x distribution back in those days because I couldn't achieve certain tasks on Windows NT 4.0 without spending a fortune. OpenELEC Mediacenter Next, Selven gave us decent introduction on OpenELEC: Open Embedded Linux Entertainment Center (OpenELEC) is a small Linux distribution built from scratch as a platform to turn your computer into an XBMC media center. OpenELEC is designed to make your system boot fast, and the install is so easy that anyone can turn a blank PC into a media machine in less than 15 minutes. I didn't know about it until this presentation. In the past, I was mainly attached to Video Disk Recorder (VDR) as it allows the use of satellite receiver cards very easily. Hm, somehow I'm still missing my precious HTPC that I had to leave back in Germany years ago. It was great piece of hardware and software; self-built PC in a standard HiFi-sized (43cm) black desktop casing with 2 full-featured Hauppauge DVB-s cards, an old-fashioned Voodoo graphics card, WiFi card, Pioneer slot-in DVD drive, and fully remote controlled via infra-red thanks to Debian, VDR and LIRC. With EP Guide, scheduled recordings and general multimedia centre it offered all the necessary comfort in the living room, besides a Nintendo game console; actually a GameCube at that time... But I have to admit that putting OpenELEC on a Raspberry Pi would be a cool DIY project in the near future. LUGM - our next generation of linux users (15.06.2013) Project Evil Genius (PEG) Don't be scared of the paragraph header. Ish gave us a cool explanation why he named it PEG - Project Evil Genius; it's because of the time of the day when he was scripting down his ideas to be able to build, package and provide software applications to various Linux distributions. The main influence came from openSuSE but the platform didn't cater for his needs and ideas, so he started to work out something on his own. During his passionate session he also talked about the amazing experience he had due to other Linux users from all over the world. During the next couple of days Ish promised to put his script to GitHub... Looking forward to that. Check out Ish's personal blog over at hacklog.in. Highly recommended to read. Why India? Simply because the registration fees per year for an Indian domain are approximately 20 times less than for a Mauritian domain (.mu). Exploring the beach of L'Escalier af the meeting 'After-party' at the beach of L'Escalier Puh, after such interesting sessions, ideas around Linux and good conversation during the breaks and over lunch it was time for a little break-out. Selven suggested that we all should head down to the beach of L'Escalier and get some impressions of nature down here in the south of the island. Talking about 'beach' ;-) - absolutely not comparable to the white-sanded ones here in Flic en Flac... There are no lagoons down at the south coast of Mauriitus, and watching the breaking waves is a different experience and joy after all. Unfortunately, I was a little bit worried about the thoughtless littering at such a remote location. You have to drive on natural paths through the sugar cane fields and I was really shocked by the amount of rubbish lying around almost everywhere. Sad, really sad and it concurs with Yasir's recent article on the same topic. Resumé & outlook It was a great event. I met with new people, had some good conversations, and even my children enjoyed themselves the whole day. The location was well-chosen, enough space for each and everyone, parking spaces and even a playground for the children. Also, a big "Thank You" to Selven and his helpers for the organisation and preparation of lunch. I'm kind of sure that this was an exceptional meeting of LUGM and I'm really looking forward to the next gathering of Linux geeks. Hopefully, soon. All images are courtesy of Avinash Meetoo. More pictures are available on Flickr.

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• ANTS CLR and Memory Profiler In Depth Review (Part 2 of 2 &ndash; Memory Profiler)

  - by ToStringTheory

  One of the things that people might not know about me, is my obsession to make my code as efficient as possible. Many people might not realize how much of a task or undertaking that this might be, but it is surely a task as monumental as climbing Mount Everest, except this time it is a challenge for the mind… In trying to make code efficient, there are many different factors that play a part – size of project or solution, tiers, language used, experience and training of the programmer, technologies used, maintainability of the code – the list can go on for quite some time. I spend quite a bit of time when developing trying to determine what is the best way to implement a feature to accomplish the efficiency that I look to achieve. One program that I have recently come to learn about – Red Gate ANTS Performance (CLR) and Memory profiler gives me tools to accomplish that job more efficiently as well. In this review, I am going to cover some of the features of the ANTS memory profiler set by compiling some hideous example code to test against. Notice As a member of the Geeks With Blogs Influencers program, one of the perks is the ability to review products, in exchange for a free license to the program. I have not let this affect my opinions of the product in any way, and Red Gate nor Geeks With Blogs has tried to influence my opinion regarding this product in any way. Introduction – Part 2 In my last post, I reviewed the feature packed Red Gate ANTS Performance Profiler.  Separate from the Red Gate Performance Profiler is the Red Gate ANTS Memory Profiler – a simple, easy to use utility for checking how your application is handling memory management…  A tool that I wish I had had many times in the past.  This post will be focusing on the ANTS Memory Profiler and its tool set. The memory profiler has a large assortment of features just like the Performance Profiler, with the new session looking nearly exactly alike: ANTS Memory Profiler Memory profiling is not something that I have to do very often…  In the past, the few cases I’ve had to find a memory leak in an application I have usually just had to trace the code of the operations being performed to look for oddities…  Sadly, I have come across more undisposed/non-using’ed IDisposable objects, usually from ADO.Net than I would like to ever see.  Support is not fun, however using ANTS Memory Profiler makes this task easier.  For this round of testing, I am going to use the same code from my previous example, using the WPF application. This time, I will choose the ‘Profile Memory’ option from the ANTS menu in Visual Studio, which launches the solution in its currently configured state/start-up project, and then launches the ANTS Memory Profiler to help.  It prepopulates all of the fields with the current project information, and all I have to do is select the ‘Start Profiling’ option. When the window comes up, it is actually quite barren, just giving ideas on how to work the profiler.  You start by getting to the point in your application that you want to profile, and then taking a ‘Memory Snapshot’.  This performs a full garbage collection, and snapshots the managed heap.  Using the same WPF app as before, I will go ahead and take a snapshot now. As you can see, ANTS is already giving me lots of information regarding the snapshot, however this is just a snapshot.  The whole point of the profiler is to perform an action, usually one where a memory problem is being noticed, and then take another snapshot and perform a diff between them to see what has changed.  I am going to go ahead and generate 5000 primes, and then take another snapshot: As you can see, ANTS is already giving me a lot of new information about this snapshot compared to the last.  Information such as difference in memory usage, fragmentation, class usage, etc…  If you take more snapshots, you can use the dropdown at the top to set your actual comparison snapshots. If you beneath the timeline, you will see a breadcrumb trail showing how best to approach profiling memory using ANTS.  When you first do the comparison, you start on the Summary screen.  You can either use the charts at the bottom, or switch to the class list screen to get to the next step.  Here is the class list screen: As you can see, it lists information about all of the instances between the snapshots, as well as at the bottom giving you a way to filter by telling ANTS what your problem is.  I am going to go ahead and select the Int16[] to look at the Instance Categorizer Using the instance categorizer, you can travel backwards to see where all of the instances are coming from.  It may be hard to see in this image, but hopefully the lightbox (click on it) will help: I can see that all of these instances are rooted to the application through the UI TextBlock control.  This image will probably be even harder to see, however using the ‘Instance Retention Graph’, you can trace an objects memory inheritance up the chain to see its roots as well.  This is a simple example, as this is simply a known element.  Usually you would be profiling an actual problem, and comparing those differences.  I know in the past, I have spotted a problem where a new context was created per page load, and it was rooted into the application through an event.  As the application began to grow, performance and reliability problems started to emerge.  A tool like this would have been a great way to identify the problem quickly. Overview Overall, I think that the Red Gate ANTS Memory Profiler is a great utility for debugging those pesky leaks.  3 Biggest Pros: Easy to use interface with lots of options for configuring profiling session Intuitive and helpful interface for drilling down from summary, to instance, to root graphs ANTS provides an API for controlling the profiler. Not many options, but still helpful. 2 Biggest Cons: Inability to automatically snapshot the memory by interval Lack of complete integration with Visual Studio via an extension panel Ratings Ease of Use (9/10) – I really do believe that they have brought simplicity to the once difficult task of memory profiling.  I especially liked how it stepped you further into the drilldown by directing you towards the best options. Effectiveness (10/10) – I believe that the profiler does EXACTLY what it purports to do.  Features (7/10) – A really great set of features all around in the application, however, I would like to see some ability for automatically triggering snapshots based on intervals or framework level items such as events. Customer Service (10/10) – My entire experience with Red Gate personnel has been nothing but good.  their people are friendly, helpful, and happy! UI / UX (9/10) – The interface is very easy to get around, and all of the options are easy to find.  With a little bit of poking around, you’ll be optimizing Hello World in no time flat! Overall (9/10) – Overall, I am happy with the Memory Profiler and its features, as well as with the service I received when working with the Red Gate personnel.  Thank you for reading up to here, or skipping ahead – I told you it would be shorter!  Please, if you do try the product, drop me a message and let me know what you think!  I would love to hear any opinions you may have on the product. Code Feel free to download the code I used above – download via DropBox

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• Nokia Windows Phone 8 App Collection

  - by Tim Murphy

  I recently upgraded to a Nokia Lumia 920.  Along with it came the availability of a number of Nokia developed apps or apps that Nokia has made available from other developers.  Below is a summary of some of the ones that I have used to this point.  There are quite a few of them so I won’t be covering everything that is available. Nokia Maps I am quite pleased with the accuracy of Nokia Maps and not having to tap the screen for each turn any more.  The information on the screen is quite good as well.  The couple of improvements I would like to see are for the voice directions to include which street or exit you need to use and improve the search accuracy.  Bing maps had much better search results in my opinion. Nokia Drive This one really had me confused when I first setup the phone.  I was driving down the road and suddenly I am getting notification tones, but there were no visual notifications on the phone.  It seems that in their infinite wisdom Nokia thinks I don’t know when I am going over the speed limit and need to be told. ESPN I really liked my ESPN app on Windows Phone 7.5, but I am not getting the type of experience I was looking for out of this app.  While it allows me to pick my favorite teams, but there isn’t a pivot page or panorama page that shows a summary of my favorite teams.  I have also found that the live tile don’t update very often.  Over all I am rather disappointed compared app produced by ESPN. Smart Shoot I really need to get the kids to let me use this on.  I like the concept, but I need to spend more time with it.  The idea how running the camera through a continuous shooting mode and then picking the best is something that I have done with my DSLR and am glad to see it available here. Cinemagraph Here is a fun filter.  It doesn’t have the most accurate editing features, but it is fun to stop certain parts of a scene and let other parts move.  As a test I stopped the traffic on the highway and let the traffic on the frontage road flow.  It makes for a fun effect.  If nothing else it could be great for sending prank animations to your friends. YouSendIt I have only briefly touched this application.  What I don’t understand is why it is needed.  Most of the functionality seems to be similar to SkyDrive and it gives you less storage.  They only feature that seems to differentiate the app is the signature capability. Creative Studio This app has some nice quick edits, but it is not very comprehensive.  I am also not to thrilled with the user experience.  It puts you though an initial color cast series that I’m not sure why it is there.  Discovery of the remaining adjustments isn’t that great.  In the end I found myself wanting Thumbia back. Panorama This is one of the apps that I like.  I found it easy to use as it guides you with a target circle that you center for it to take the next pictures.  It also stitches the images with amazing speed.  The one thing I wish it had was the capability to turn the phone into portrait orientation and do a taller panorama.  Perhaps we will see this in the future. Nokia Music After getting over the missing album art I found that there were a number of missing features with this app as well.  I have a Zune HD and I am used to being able to go through my collection and adding songs, albums or artists to my now playing.  There also doesn’t seem to be a way to manage playlists that I have seen yet.  Other than that the UI is familiar and it give Nokia City Lens Augmented reality is a cool concept, but I still haven’t seen it implemented in a compelling fashion beyond a demo at TED a couple of years ago.  The app still leaves me wanting as well.  It does give an interesting toy.  It gives you the ability to look for general categories and see general direction and clusters of locations.  I think as this concept is better thought out it will become more compelling. Nokia Trailers I don’t know how often I will use this app, but I do like being able to see what movies are being promoted.  I can’t wait for The Hobbit to come out and the trailer was just what the doctor ordered.  I can see coming back to this app from time to time. PhotoBeamer PhotoBeamer is a strange beast that needs a better instruction manual.  It seems a lot like magic but very confusing.  I need some more testing, but I don’t think this is something that most people are going to understand quickly and may give up before getting it to work.  I may put an update here after playing with it further. Ringtone Maker The app was just published and it didn’t work very well for me. It couldn’t find 95% of the songs that Nokia Music was playing for me and crashed several times.  It also had songs named wrong that when I checked them in Nokia Music they were fine.  This app looks like it has a long way to go. Summary In all I think that Nokia is offering a well rounded set of initial applications that can get any new owner started.  There is definitely room for improvement in all of these apps.  The main need is usability upgrades.  I would guess that with feedback from users they will come up to acceptable levels.  Try them out and see if you agree. del.icio.us Tags: Windows Phone,Nokia,Lumia,Nokia Apps,ESPN,PhotoBeamer,City Lens,YouSendIt,Drive,Maps

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• Open source CMS for a university department

  - by Greg Kuperberg

  I realize that this type of question gets asked over and over again. Nonetheless, I want to ask a more specific version. I'm in a university math department. Long ago our sysadmins (or just one at the time) switched to a web content management system. At the time, Zope looked like an informed choice. We have used Zope for years, but at least in my opinion, it has always been a controversial decision. At the time I didn't understand why it was so important to have a web CMS. Now I see that it certainly is important, but I don't know that it should be Zope. The good (even necessary) features of Zope for us are: It's free and Linux-based. It is a true CMS and not something else (e.g. wiki or blog) It lets you write HTML and scripts. What I really don't like about Zope is that the outcome of using it is all-or-nothing in a lot of ways. At least in convenient use, it ends up dividing the enterprise into superusers who can do everything, and lusers who can't do anything (except write their own home pages in plain HTML). It has a huge user manual, which end users won't have time to read. Somehow with the access permissions, the simple thing to do is to let a few admins access all of the source and data and that's it. Since this is a math department, the user base varies from real novices to people who understand computers reasonably well. But as it stands, any change that involves Zope has to go through the sysadmins. When the sysadmins are in a hurry, sometimes they will also just add plain HTML pages to the web site instead of using the Zope framework. It doesn't help matters that Zope is fairly disk-intensive and fairly hype-intensive. Not to dwell on Zope too much, but I am wondering what is the right web CMS for a mixed user base of terminal novices, quick studies, and experienced users. Some users might want intermediate permissions, e.g. read permission but not write permission, or permission to change some subset of the pages or see some subset of the database tables. Also it should be Linux-based and open source and a little bit scalable, and of course widely used and well-supported is a good idea. I might guess that the answer is Drupal just because that was the general answer before, but I don't know if it is the right type of CMS for this purpose. (But note that Python is a relatively popular language in a math department, among other reasons because Sage is based on Python.) I can see that I didn't completely define the question and that people are guessing what type of site it is. It is the UC Davis Math Department. The main structure of the site is not suitable for a wiki and it is also not the same thing as a course environment like Moodle. Rather, the site is mostly structured as a generic medium-small enterprise. Some components of the site could be a wiki, Moodle, LaTeX plugin, Request Tracker, etc. However, the main issue is not these components. The main issue is that it would be better to decentralize management of the site. Right now, everything that is in the Zope CMS has to go through the sysadmins. Every other user in the department either has to put in a request to them, or write their own web pages with no help from Zope. There are two main reasons for this: (1) Other people in the department don't have time to read the Zope manual. (2) It's a hassle to set up intermediate permissions in Zope. However, there are other people in the department who know how to write computer programs and use markup languages. I wouldn't want a solution that assumes that users either can't be trusted with much more than drag-and-drop, or that they are IT professionals who sleep with documentation manuals. I'm wondering if Plone/Zope still has this quality, since certainly Zope by itself does. But I also wonder sometimes if common-sense flexibility is unfashionable these days, and that things in general have be either mindlessly easy or incredibly powerful.

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• Weighted round robins via TTL - possible?

  - by Joe Hopfgartner

  I currently use DNS round robin for load balancing, which works great. The records look like this (I have a ttl of 120 seconds) ;; ANSWER SECTION: orion.2x.to. 116 IN A 80.237.201.41 orion.2x.to. 116 IN A 87.230.54.12 orion.2x.to. 116 IN A 87.230.100.10 orion.2x.to. 116 IN A 87.230.51.65 I learned that not every ISP / device treats such a response the same way. For example some DNS servers rotate the addresses randomly or always cycle them through. Some just propagate the first entry, others try to determine which is best (regionally near) by looking at the ip address. However if the userbase is big enough (spreads over multiple ISPs etc) it balances pretty well. The discrepancies from highest to lowest loaded server hardly every exceeds 15%. However now I have the problem that I am introducing more servers into the systems, that not all have the same capacities. I currently only have 1gbps servers, but I want to work with 100mbit and also 10gbps servers too. So what I want is I want to introduce a server with 10 GBps with a weight of 100, a 1 gbps server with a weight of 10 and a 100 mbit server with a weight of 1. I used to add servers twice to bring more traffic to them (which worked nice. the bandwidth doubled almost.) But adding a 10gbit server 100 times to DNS is a bit rediculous. So I thought about using the TTL. If I give server A 240 seconds ttl and server B only 120 seconds (which is about about the minimum to use for round robin, as a lot of dns servers set to 120 if a lower ttl is specified.. so i have heard) I think something like this should occour in an ideal scenario: first 120 seconds 50% of requests get server A -> keep it for 240 seconds. 50% of requests get server B -> keep it for 120 seconds second 120 seconds 50% of requests still have server A cached -> keep it for another 120 seconds. 25% of requests get server A -> keep it for 240 seconds 25% of requests get server B -> keep it for 120 seconds third 120 seconds 25% will get server A (from the 50% of Server A that now expired) -> cache 240 sec 25% will get server B (from the 50% of Server A that now expired) -> cache 120 sec 25% will have server A cached for another 120 seconds 12.5% will get server B (from the 25% of server B that now expired) -> cache 120sec 12.5% will get server A (from the 25% of server B that now expired) -> cache 240 sec fourth 120 seconds 25% will have server A cached -> cache for another 120 secs 12.5% will get server A (from the 25% of b that now expired) -> cache 240 secs 12.5% will get server B (from the 25% of b that now expired) -> cache 120 secs 12.5% will get server A (from the 25% of a that now expired) -> cache 240 secs 12.5% will get server B (from the 25% of a that now expired) -> cache 120 secs 6.25% will get server A (from the 12.5% of b that now expired) -> cache 240 secs 6.25% will get server B (from the 12.5% of b that now expired) -> cache 120 secs 12.5% will have server A cached -> cache another 120 secs ... i think i lost something at this point but i think you get the idea.... As you can see this gets pretty complicated to predict and it will for sure not work out like this in practice. But it should definitely have an effect on the distribution! I know that weighted round robin exists and is just controlled by the root server. It just cycles through dns records when responding and returns dns records with a set propability that corresponds to the weighting. My DNS server does not support this, and my requirements are not that precise. If it doesnt weight perfectly its okay, but it should go into the right direction. I think using the TTL field could be a more elegant and easier solution - and it deosnt require a dns server that controls this dynamically, which saves resources - which is in my opinion the whole point of dns load balancing vs hardware load balancers. My question now is... are there any best prectices / methos / rules of thumb to weight round robin distribution using the TTL attribute of DNS records? Edit: The system is a forward proxy server system. The amount of Bandwidth (not requests) exceeds what one single server with ethernet can handle. So I need a balancing solution that distributes the bandwidth to several servers. Are there any alternative methods than using DNS? Of course I can use a load balancer with fibre channel etc, but the costs are rediciulous and it also increases only the width of the bottleneck and does not eliminate it. The only thing i can think of are anycast (is it anycast or multicast?) ip addresses, but I don't have the means to set up such a system.

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• Understanding Node.js and concept of non-blocking I/O

  - by Saif Bechan

  Recently I became interested in using Node.js to tackle some of the parts of my web-application. I love the part that its full JavaScript and its very light weight so no use anymore to call an JavaScript-PHP call but a lighter JavaScript-JavaScript call. I however do not understand all the concepts explained. Basic concepts Now in the presentation for Node.js Ryan Dahl talks about non-blocking IO and why this is the way we need to create our programs. I can understand the theoretical concept. You just don't wait for a response, you go ahead and do other things. You make a callback for the response, and when the response arrives millions of clock-cycles later, you can fire that. If you have not already I recommend to watch this presentation. It is very easy to follow and pretty detailed. There are some nice concepts explained on how to write your code in a good manner. There are also some examples given and I am going to work with the basic example given. Examples The way we do thing now: puts("Enter your name: "); var name = gets(); puts("Name: " + name); Now the problem with this is that the code is halted at line 1. It blocks your code. The way we need to do things according to node puts("Enter your name: "); gets(function (name) { puts("Name: " + name); }); Now with this your program does not halt, because the input is a function within the output. So the programs continues to work without halting. Questions Now the basic question I have is how does this work in real-life situations. I am talking here for the use in web-applications. The application I am writing does I/O, bit is still does it in am blocking matter. I think that most of the time, if not all, you need to block, because you have to wait on what the response is you have to work with. When you need to get some information from the database, most of the time this data needs to be verified before you can further with the code. Example 1 If you take a login for example. You have to wait for the database to response to return, because you can not do anything else. I can't see a way around this without blocking. Example 2 Going back to the basic example. The use just request something from a database which does not need any verification. You still have to block because you don't have anything to do more. I can not come up with a single example where you want to do other things while you wait for the response to return. Possible answers I have read that this frees up recourses. When you program like this it takes less CPU or memory usage. So this non-blocking IO is ONLY meant to free up recourses and does not have any other practical use. Not that this is not a huge plus, freeing up recourses is always good. Yet I fail to see this as a good solution. because in both of the above examples, the program has to wait for the response of the user. Whether this is inside a function, or just inline, in my opinion there is a program that wait for input. Resources I looked at I have looked at some recourses before I posted this question. They talk a lot about the theoretical concept, which is quite clear. Yet i fail to see some real-life examples where this is makes a huge difference. Stackoverflow: What is in simple words blocking IO and non-blocking IO? Blocking IO vs non-blocking IO; looking for good articles tidy code for asynchronous IO Other recources: Wikipedia: Asynchronous I/O Introduction to non-blocking I/O The C10K problem

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• JS: using 'var me = this' to reference an object instead of using a global array

  - by Marco Demaio

  The example below, is just an example, I know that I don't need an object to show an alert box when user clicks on div blocks, but it's just a simple example to explain a situation that frequently happens when writing JS code. In the example below I use a globally visible array of objects to keep a reference to each new created HelloObject, in this way events called when clicking on a div block can use the reference in the arry to call the HelloObject's public function hello(). 1st have a look at the code: <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> <html><head><meta http-equiv="Content-Type" content="text/html; charset=windows-1252"> <title>Test </title> <script type="text/javascript"> /***************************************************** Just a cross browser append event function, don't need to understand this one to answer my question *****************************************************/ function AppendEvent(html_element, event_name, event_function) {if(html_element) {if(html_element.attachEvent) html_element.attachEvent("on" + event_name, event_function); else if(html_element.addEventListener) html_element.addEventListener(event_name, event_function, false); }} /****************************************************** Just a test object ******************************************************/ var helloobjs = []; var HelloObject = function HelloObject(div_container) { //Adding this object in helloobjs array var id = helloobjs.length; helloobjs[id] = this; //Appending click event to show the hello window AppendEvent(div_container, 'click', function() { helloobjs[id].hello(); //THIS WORKS! }); /***************************************************/ this.hello = function() { alert('hello'); } } </script> </head><body> <div id="one">click me</div> <div id="two">click me</div> <script type="text/javascript"> var t = new HelloObject(document.getElementById('one')); var t = new HelloObject(document.getElementById('two')); </script> </body></html> In order to achive the same result I could simply replace the code //Appending click event to show the hello window AppendEvent(div_container, 'click', function() { helloobjs[id].hello(); //THIS WORKS! }); with this code: //Appending click event to show the hello window var me = this; AppendEvent(div_container, 'click', function() { me.hello(); //THIS WORKS TOO AND THE GLOBAL helloobjs ARRAY BECOMES SUPEFLOUS! }); thus would make the helloobjs array superflous. My question is: does this 2nd option in your opinion create memoy leaks on IE or strange cicular references that might lead to browsers going slow or to break??? I don't know how to explain, but coming from a background as a C/C++ coder, doing in this 2nd way sounds like a some sort of circular reference that might break memory at some point. I also read on internet about the IE closures memory leak issue http://jibbering.com/faq/faq_notes/closures.html (I don't know if it was fixed in IE7 and if yes, I hope it does not come out again in IE8). Thanks

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• swfobject weird behavior

  - by David

  Hi All, I'm using swfobject to embed my flash. It's doing weird things. I've created a simple textfield using FlexBuilder. It's an AS3 project, which extends Sprite. I've set its width to be 640 and height to 450. Then, in the swfobject parameters of the page, I've also set 640 x 450. I've made the background nice and red and ugly so you can see it. :) http://www.brighttext.com/flash/TextFieldSetFormat.html It seems to be the right dimensions. BUT I've got a textfield which is supposed to be almost the same size and height. This runs fine in FlexBuilder (is the right size) but is all messed up once I add swfobject Can anyone see what is happening? EDIT NOTE: I just looked at it and it looks ok. But then I refreshed the page and the textfield is postage-stamp size (again -- this is the original behavior I saw.) It's now looking OK in firefox but not in IE8. Flash is supposed to look the same in all browsers !!?? AS3 code: package { import flash.display.Sprite; import flash.text.TextField; import flash.text.TextFormat; import flash.text.Font; [SWF(width="640", height="450", backgroundColor="#FFFFFF", frameRate="30")] public class TextFieldSetFormat extends Sprite { [Embed(source='C:/WINDOWS/Fonts/ArialBD.TTF', fontWeight = 'bold', fontName='ArialBold')] [Embed(source='C:/WINDOWS/Fonts/Arial.TTF', fontWeight = 'regular', fontName='Arial')] public function TextFieldSetFormat() { var tf2:TextFormat = new TextFormat(); tf2.size = 16; tf2.font = "Arial"; Font.registerFont(_VerdanaFontBold); Font.registerFont(_VerdanaFont); var pad:Number = 10; var brightTextField:TextField = new TextField; brightTextField.backgroundColor = 0xDDF3B2; brightTextField.background = true; brightTextField.embedFonts = true; brightTextField.border = true; brightTextField.defaultTextFormat = tf2; brightTextField.wordWrap = true; brightTextField.multiline = true; brightTextField.width = stage.stageWidth - (4 * pad); brightTextField.height = stage.stageHeight - (3 * pad); brightTextField.x = 2*pad; brightTextField.y = 2*pad; brightTextField.text = "Dear Senators, I have become concerned over the idea that some in the Senate will oppose the public option because of a group of wild-eyed, overbearing but misinformed ideologues. These people mistakenly equate insurance reform with Socialism and call our first African-American President unprintable epithets. This is unacceptable. The public option is the choice of more than 70% of Americans, a majority of the House and a great many opinion leaders. Passing insurance reform without a public option persists the current broken system. I am aware that many Senators would prefer to pass a reform bill with bipartisan support. But we cannot allow this critical debate to be hijacked by extremists or corporate profiteers. Thank you, and I look forward to hearing from you."; addChild(brightTextField); } } }

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• The best cross platform (portable) arbitrary precision math library

  - by Siu Ching Pong - Asuka Kenji

  Dear ninjas / hackers / wizards, I'm looking for a good arbitrary precision math library in C or C++. Could you please give me some advices / suggestions? The primary requirements: It MUST handle arbitrarily big integers (my primary interest is on integers). In case that you don't know what the word arbitrarily big means, imagine something like 100000! (the factorial of 100000). The precision MUST NOT NEED to be specified during library initialization / object creation. The precision should ONLY be constrained by the available resources of the system. It SHOULD utilize the full power of the platform, and should handle "small" numbers natively. That means on a 64-bit platform, calculating 2^33 + 2^32 should use the available 64-bit CPU instructions. The library SHOULD NOT calculate this in the same way as it does with 2^66 + 2^65 on the same platform. It MUST handle addition (+), subtraction (-), multiplication (*), integer division (/), remainder (%), power (**), increment (++), decrement (--), gcd(), factorial(), and other common integer arithmetic calculations efficiently. Ability to handle functions like sqrt() (square root), log() (logarithm) that do not produce integer results is a plus. Ability to handle symbolic computations is even better. Here are what I found so far: Java's BigInteger and BigDecimal class: I have been using these so far. I have read the source code, but I don't understand the math underneath. It may be based on theories / algorithms that I have never learnt. The built-in integer type or in core libraries of bc / Python / Ruby / Haskell / Lisp / Erlang / OCaml / PHP / some other languages: I have ever used some of these, but I have no idea on which library they are using, or which kind of implementation they are using. What I have already known: Using a char as a decimal digit, and a char* as a decimal string and do calculations on the digits using a for-loop. Using an int (or a long int, or a long long) as a basic "unit" and an array of it as an arbitrary long integer, and do calculations on the elements using a for-loop. Booth's multiplication algorithm What I don't know: Printing the binary array mentioned above in decimal without using naive methods. Example of a naive method: (1) add the bits from the lowest to the highest: 1, 2, 4, 8, 16, 32, ... (2) use a char* string mentioned above to store the intermediate decimal results). What I appreciate: Good comparisons on GMP, MPFR, decNumber (or other libraries that are good in your opinion). Good suggestions on books / articles that I should read. For example, an illustration with figures on how a un-naive arbitrarily long binary to decimal conversion algorithm works is good. Any help. Please DO NOT answer this question if: you think using a double (or a long double, or a long long double) can solve this problem easily. If you do think so, it means that you don't understand the issue under discussion. you have no experience on arbitrary precision mathematics. Thank you in advance! Asuka Kenji

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• A format for storing personal contacts in a database

  - by Gart

  I'm thinking of the best way to store personal contacts in a database for a business application. The traditional and straightforward approach would be to create a table with columns for each element, i.e. Name, Telephone Number, Job title, Address, etc... However, there are known industry standards for this kind of data, like for example vCard, or hCard, or vCard-RDF/XML or even Windows Contacts XML Schema. Utilizing an standard format would offer some benefits, like inter-operablilty with other systems. But how can I decide which method to use? The requirements are mainly to store the data. Search and ordering queries are highly unlikely but possible. The volume of the data is 100,000 records at maximum. My database engine supports native XML columns. I have been thinking to use some XML-based format to store the personal contacts. Then it will be possible to utilize XML indexes on this data, if searching and ordering is needed. Is this a good approach? Which contacts format and schema would you recommend for this? Edited after first answers Here is why I think the straightforward approach is bad. This is due to the nature of this kind of data - it is not that simple. The personal contacts it is not well-structured data, it may be called semi-structured. Each contact may have different data fields, maybe even such fields which I cannot anticipate. In my opinion, each piece of this data should be treated as important information, i.e. no piece of data could be discarded just because there was no relevant column in the database. If we took it further, assuming that no data may be lost, then we could create a big text column named Comment or Description or Other and put there everything which cannot be fitted well into table columns. But then again - the data would lose structure - this might be bad. If we wanted structured data then - according to the database design principles - the data should be decomposed into entities, and relations should be established between the entities. But this adds complexity - there are just too many entities, and lots of design desicions should be made, like "How do we store Address? Personal Name? Phone number? How do we encode home phone numbers and mobile phone numbers? How about other contact info?.." The relations between entities are complex and multiple, and each relation is a table in the database. Each relation needs to be documented in the design papers. That is a lot of work to do. But it is possible to avoid the complexity entirely - just document that the data is stored according to such and such standard schema, period. Then anybody who would be reading that document should easily understand what it was all about. Finally, this is all about using an industry standard. The standard is, hopefully, designed by some clever people who anticipated and described the structure of personal contacts information much better than I ever could. Why should we all reinvent the wheel?? It's much easier to use a standard schema. The problem is, there are just too many standards - it's not easy to decide which one to use!

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• If 'Architect' is a dirty word - what's the alternative; when not everyone can actually design a goo

  - by Andras Zoltan

  Now - I'm a developer first and foremost; but whenever I sit down to work on a big project with lots of interlinking components and areas, I will forward-plan my interfaces, base classes etc as best I can - putting on my Architect hat. For a few weeks I've been doing this for a huge project - designing whole swathes of interfaces etc for a business-wide platform that we're developing. The basic structure is a couple of big projects that consists of service and data interfaces, with some basic implementations of all of these. On their own, these assemblies are useless though, as they are simply intended intended as a scaffold on which to build a business-specific implementation (we have a lot of businesses). Therefore, the design of the core platform is absolutely crucial, since consumers of the system are not intended to know which implementation they are actually using. In the past it's not worked so well, but after a few proof-of-concepts and R&D projects this new platform is now growing nicely and is already proving itself. Then somebody else gets involved in the project - he's a TDD man who sees code-level architecture as an irrelevance and is definitely from the camp that 'architect' is a dirty word - I should add that our working relationship is very good despite this :) He's open about the fact that he can't architect in advance and obviously TDD really helps him because it allows him to evolve his systems over time. That I get, and totally understand; but it means that his coding style, basically, doesn't seem to be able to honour the architecture that I've been putting in place. Now don't get me wrong - he's an awesome coder; but the other day he needed to extend one of his components (an implementation of a core interface) to bring in an extra implementation-specific dependency; and in doing so he extended the core interface as well as his implementation (he uses ReSharper), thus breaking the independence of the whole interface. When I pointed out his error to him, he was dismayed. Being test-first, all that mattered to him was that he'd made his tests pass, and just said 'well, I need that dependency, so can't we put it in?'. Of course we could put it in, but I was frustrated that he couldn't see that refactoring the generic interface to incorporate an implementation-specific feature was just wrong! But it is all very Charlie Brown to him (you know the sound the adults make when they're talking to the children) - as far as he's concerned we don't need to worry about it because we can always refactor. The problem is, the culture of test-write-refactor is all very well and good - but not when you're dealing with a platform that is going to be shared out among so many projects that you could never get them all in one place to make the refactorings work. In my opinion, sometimes you actually have to think about what you're doing, and not just let nature take its course. Am I simply fulfilling the role of Architect as a dirty word here? I believe that architecture is important and should be thought about before code gets written; unless it's a particularly small project. But when you're working in a team of people who don't think that way, or even can't think that way how can you actually get this across? Is it a case of simply making the architecture off-limits to changes by other people? I don't want to start having bloody committees just to be able to grow the system; but equally I don't want to be the only one responsible for it all. Do you think the architect role is a waste of time? Is it at odds with TDD and other practises? Can this mix of different practises be made to work, or should I just be a lot less precious (and in so doing allow a generic platform become useless!)? Or do I just lay down the law? Any ideas/experiences/views gratefully received.

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• Writing a code example

  - by Stefano Borini

  I would like to have your feedback regarding code examples. One of the most frustrating experiences I sometimes have when learning a new technology is finding useless examples. I think an example as the most precious thing that comes with a new library, language, or technology. It must be a starting point, a wise and unadulterated explanation on how to achieve a given result. A perfect example must have the following characteristics: Self contained: it should be small enough to be compiled or executed as a single program, without dependencies or complex makefiles. An example is also a strong functional test if you correctly installed the new technology. The more issues could arise, the more likely is that something goes wrong, and the more difficult is to debug and solve the situation. Pertinent: it should demonstrate one, and only one, specific feature of your software/library, involving the minimal additional behavior from external libraries. Helpful: the code should bring you forward, step by step, using comments or self-documenting code. Extensible: the example code should be a small “framework” or blueprint for additional tinkering. A learner can start by adding features to this blueprint. Recyclable: it should be possible to extract parts of the example to use in your own code Easy: An example code is not the place to show your code-fu skillz. Keep it easy. helpful acronym: SPHERE. Prototypical examples of violations of those rules are the following: Violation of self-containedness: an example spanning multiple files without any real need for it. If your example is a python program, keep everything into a single module file. Don’t sub-modularize it. In Java, try to keep everything into a single class, unless you really must partition some entity into a meaningful object you need to pass around (and java mandates one class per file, if I remember correctly). Violation of Pertinency: When showing how many different shapes you can draw, adding radio buttons and complex controls with all the possible choices for point shapes is a bad idea. You de-focalize your example code, introducing code for event handling, controls initialization etc., and this is not part the feature you want to demonstrate, they are unnecessary noise in the understanding of the crucial mechanisms providing the feature. Violation of Helpfulness: code containing dubious naming, wrong comments, hacks, and functions longer than one page of code. Violation of Extensibility: badly factored code that have everything into a single function, with potentially swappable entities embedded within the code. Example: if an example reads data from a file and displays it, create a method getData() returning a useful entity, instead of opening the file raw and plotting the stuff. This way, if the user of the library needs to read data from a HTTP server instead, he just has to modify the getData() module and use the example almost as-is. Another violation of Extensibility comes if the example code is not under a fully liberal (e.g. MIT or BSD) license. Violation of Recyclability: when the code layout is so intermingled that is difficult to easily copy and paste parts of it and recycle them into another program. Again, licensing is also a factor. Violation of Easiness: Yes, you are a functional-programming nerd and want to show how cool you are by doing everything on a single line of map, filter and so on, but that could not be helpful to someone else, who is already under pressure to understand your library, and now has to understand your code as well. And in general, the final rule: if it takes more than 10 minutes to do the following: compile the code, run it, read the source, and understand it fully, it means that the example is not a good one. Please let me know your opinion, either positive or negative, or experience on this regard.

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• Domain Validation in a CQRS architecture

  - by Jupaol

  Basically I want to know if there is a better way to validate my domain entities. This is how I am planning to do it but I would like your opinion The first approach I considered was: class Customer : EntityBase<Customer> { public void ChangeEmail(string email) { if(string.IsNullOrWhitespace(email)) throw new DomainException(“...”); if(!email.IsEmail()) throw new DomainException(); if(email.Contains(“@mailinator.com”)) throw new DomainException(); } } I actually do not like this validation because even when I am encapsulating the validation logic in the correct entity, this is violating the Open/Close principle (Open for extension but Close for modification) and I have found that violating this principle, code maintenance becomes a real pain when the application grows up in complexity. Why? Because domain rules change more often than we would like to admit, and if the rules are hidden and embedded in an entity like this, they are hard to test, hard to read, hard to maintain but the real reason why I do not like this approach is: if the validation rules change, I have to come and edit my domain entity. This has been a really simple example but in RL the validation could be more complex So following the philosophy of Udi Dahan, making roles explicit, and the recommendation from Eric Evans in the blue book, the next try was to implement the specification pattern, something like this class EmailDomainIsAllowedSpecification : IDomainSpecification<Customer> { private INotAllowedEmailDomainsResolver invalidEmailDomainsResolver; public bool IsSatisfiedBy(Customer customer) { return !this.invalidEmailDomainsResolver.GetInvalidEmailDomains().Contains(customer.Email); } } But then I realize that in order to follow this approach I had to mutate my entities first in order to pass the value being valdiated, in this case the email, but mutating them would cause my domain events being fired which I wouldn’t like to happen until the new email is valid So after considering these approaches, I came out with this one, since I am going to implement a CQRS architecture: class EmailDomainIsAllowedValidator : IDomainInvariantValidator<Customer, ChangeEmailCommand> { public void IsValid(Customer entity, ChangeEmailCommand command) { if(!command.Email.HasValidDomain()) throw new DomainException(“...”); } } Well that’s the main idea, the entity is passed to the validator in case we need some value from the entity to perform the validation, the command contains the data coming from the user and since the validators are considered injectable objects they could have external dependencies injected if the validation requires it. Now the dilemma, I am happy with a design like this because my validation is encapsulated in individual objects which brings many advantages: easy unit test, easy to maintain, domain invariants are explicitly expressed using the Ubiquitous Language, easy to extend, validation logic is centralized and validators can be used together to enforce complex domain rules. And even when I know I am placing the validation of my entities outside of them (You could argue a code smell - Anemic Domain) but I think the trade-off is acceptable But there is one thing that I have not figured out how to implement it in a clean way. How should I use this components... Since they will be injected, they won’t fit naturally inside my domain entities, so basically I see two options: Pass the validators to each method of my entity Validate my objects externally (from the command handler) I am not happy with the option 1 so I would explain how I would do it with the option 2 class ChangeEmailCommandHandler : ICommandHandler<ChangeEmailCommand> { public void Execute(ChangeEmailCommand command) { private IEnumerable<IDomainInvariantValidator> validators; // here I would get the validators required for this command injected, and in here I would validate them, something like this using (var t = this.unitOfWork.BeginTransaction()) { var customer = this.unitOfWork.Get<Customer>(command.CustomerId); this.validators.ForEach(x =. x.IsValid(customer, command)); // here I know the command is valid // the call to ChangeEmail will fire domain events as needed customer.ChangeEmail(command.Email); t.Commit(); } } } Well this is it. Can you give me your thoughts about this or share your experiences with Domain entities validation EDIT I think it is not clear from my question, but the real problem is: Hiding the domain rules has serious implications in the future maintainability of the application, and also domain rules change often during the life-cycle of the app. Hence implementing them with this in mind would let us extend them easily. Now imagine in the future a rules engine is implemented, if the rules are encapsulated outside of the domain entities, this change would be easier to implement

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• Keyboard for programming

  - by exhuma

  This may seem a bit a tangential topic. It's not directly related to actual code, but is important for our line of work nevertheless. Over the years, I've switched keyboards a few times. All of them had slightly different key layouts. And I'm not talking about the language/locale layout, but the physical layout! Why not the locale layout? Well, quite frankly, that's easy to change via software. I personally have a German keyboard but have it set to the UK layout. Why? It's quite hard to find different layouts in the shops where I live. Even ordering is not always easy in the shops. So that leaves me with Internet shops. But I prefer to "test" my keyboards before buying. The most notable changes are: Mangled "Home Key Block" I've seen this first on a Logitech keyboard, but it may have originated elsewhere. Shape of the "Enter" key I've seen three different cases so far: Two lines high, wider at the top Two lines high, wider at the bottom One line high Shape of the Backspace button I've seen two types so far: One "character" wide Two "characters" wide OS Keys For Macs, you have the Option and Command buttons, for Windows you have the Windows and Context Menu buttons. Cherry even produced a Linux keyboard once (unfortunately I cannot find many details except news results). I assume a dedicated Linux keyboard would sport a Compose key and had the SysRq always labelled as well (note that some standard layouts do this already). Obviously... .. all these differences entail that some keys have to be moved around the board a lot. Which means, if you are used to one and have to work on another one, you happen to hit the wrong keys quite often. As it happens, this is much more annoying for programmers as it is for people who write texts. Mainly because the keys which are moved around are special character keys, often used in programming. Often these hardware layouts depend also indirectly on where you buy the keyboards. Honestly, I haven't seen a keyboard with a one-line "Enter" key in Germany, nor Luxembourg. I may just have missed it but that's how it looks to me at least. A survey I've seen some attempts at surveys in the style "which keyboard is best for programming". But they all - in my opinion - are not using comparable sets. So I was wondering if it was possible to concoct a survey taking the above criteria into account. But ignoring key dimensions that one would be a bit overkill I guess ;) From what I can see there are the following types of physical layout: Backspace: 2-characters wide Enter: 2-Lines, wider top Backspace: 2-characters wide Enter: 1-Line Backspace: 1-character wide Enter: 2-Lines, wider bottom Then there are the other possible permutations (home-key block, os-keys), which in total makes for quite a large list of categories. Now, I wonder... Would anyone be interested in such a survey? I personally would. Because I am looking for the perfect fit for me. If yes, then I could really use the help of anyone here to propose some models to include in the survey. Once I have some models for each category (I'd say at least 3 per category) I could go ahead and write up a survey, put it on-line and let the it collect data for a while. What do you think?

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• How do I use constructor dependency injection to supply Models from a collection to their ViewModels

  - by GraemeF

  I'm using constructor dependency injection in my WPF application and I keep running into the following pattern, so would like to get other people's opinion on it and hear about alternative solutions. The goal is to wire up a hierarchy of ViewModels to a similar hierarchy of Models, so that the responsibility for presenting the information in each model lies with its own ViewModel implementation. (The pattern also crops up under other circumstances but MVVM should make for a good example.) Here's a simplified example. Given that I have a model that has a collection of further models: public interface IPerson { IEnumerable<IAddress> Addresses { get; } } public interface IAddress { } I would like to mirror this hierarchy in the ViewModels so that I can bind a ListBox (or whatever) to a collection in the Person ViewModel: public interface IPersonViewModel { ObservableCollection<IAddressViewModel> Addresses { get; } void Initialize(); } public interface IAddressViewModel { } The child ViewModel needs to present the information from the child Model, so it's injected via the constructor: public class AddressViewModel : IAddressViewModel { private readonly IAddress _address; public AddressViewModel(IAddress address) { _address = address; } } The question is, what is the best way to supply the child Model to the corresponding child ViewModel? The example is trivial, but in a typical real case the ViewModels have more dependencies - each of which has its own dependencies (and so on). I'm using Unity 1.2 (although I think the question is relevant across the other IoC containers), and I am using Caliburn's view strategies to automatically find and wire up the appropriate View to a ViewModel. Here is my current solution: The parent ViewModel needs to create a child ViewModel for each child Model, so it has a factory method added to its constructor which it uses during initialization: public class PersonViewModel : IPersonViewModel { private readonly Func<IAddress, IAddressViewModel> _addressViewModelFactory; private readonly IPerson _person; public PersonViewModel(IPerson person, Func<IAddress, IAddressViewModel> addressViewModelFactory) { _addressViewModelFactory = addressViewModelFactory; _person = person; Addresses = new ObservableCollection<IAddressViewModel>(); } public ObservableCollection<IAddressViewModel> Addresses { get; private set; } public void Initialize() { foreach (IAddress address in _person.Addresses) Addresses.Add(_addressViewModelFactory(address)); } } A factory method that satisfies the Func<IAddress, IAddressViewModel> interface is registered with the main UnityContainer. The factory method uses a child container to register the IAddress dependency that is required by the ViewModel and then resolves the child ViewModel: public class Factory { private readonly IUnityContainer _container; public Factory(IUnityContainer container) { _container = container; } public void RegisterStuff() { _container.RegisterInstance<Func<IAddress, IAddressViewModel>>(CreateAddressViewModel); } private IAddressViewModel CreateAddressViewModel(IAddress model) { IUnityContainer childContainer = _container.CreateChildContainer(); childContainer.RegisterInstance(model); return childContainer.Resolve<IAddressViewModel>(); } } Now, when the PersonViewModel is initialized, it loops through each Address in the Model and calls CreateAddressViewModel() (which was injected via the Func<IAddress, IAddressViewModel> argument). CreateAddressViewModel() creates a temporary child container and registers the IAddress model so that when it resolves the IAddressViewModel from the child container the AddressViewModel gets the correct instance injected via its constructor. This seems to be a good solution to me as the dependencies of the ViewModels are very clear and they are easily testable and unaware of the IoC container. On the other hand, performance is OK but not great as a lot of temporary child containers can be created. Also I end up with a lot of very similar factory methods. Is this the best way to inject the child Models into the child ViewModels with Unity? Is there a better (or faster) way to do it in other IoC containers, e.g. Autofac? How would this problem be tackled with MEF, given that it is not a traditional IoC container but is still used to compose objects?

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• Why does this Quicksort work?

  - by IVlad

  I find this Quicksort partitioning approach confusing and wrong, yet it seems to work. I am referring to this pseudocode. Note: they also have a C implementation at the end of the article, but it's very different from their pseudocode, so I don't care about that. I have also written it in C like this, trying to stay true to the pseudocode as much as possible, even if that means doing some weird C stuff: #include <stdio.h> int partition(int a[], int p, int r) { int x = a[p]; int i = p - 1; int j = r + 1; while (1) { do j = j - 1; while (!(a[j] <= x)); do i = i + 1; while (!(a[i] >= x)); if (i < j) { int t = a[i]; a[i] = a[j]; a[j] = t; } else { for (i = 1; i <= a[0]; ++i) printf("%d ", a[i]); printf("- %d\n", j); return j; } } } int main() { int a[100] = //{8, 6,10,13,15,8,3,2,12}; {7, 7, 6, 2, 3, 8, 4, 1}; partition(a, 1, a[0]); return 0; } If you run this, you'll get the following output: 1 6 2 3 4 8 7 - 5 However, this is wrong, isn't it? Clearly a[5] does not have all the values before it lower than it, since a[2] = 6 > a[5] = 4. Not to mention that 7 is supposed to be the pivot (the initial a[p]) and yet its position is both incorrect and lost. The following partition algorithm is taken from wikipedia: int partition2(int a[], int p, int r) { int x = a[r]; int store = p; for (int i = p; i < r; ++i) { if (a[i] <= x) { int t = a[i]; a[i] = a[store]; a[store] = t; ++store; } } int t = a[r]; a[r] = a[store]; a[store] = t; for (int i = 1; i <= a[0]; ++i) printf("%d ", a[i]); printf("- %d\n", store); return store; } And produces this output: 1 6 2 3 8 4 7 - 1 Which is a correct result in my opinion: the pivot (a[r] = a[7]) has reached its final position. However, if I use the initial partitioning function in the following algorithm: void Quicksort(int a[], int p, int r) { if (p < r) { int q = partition(a, p, r); // initial partitioning function Quicksort(a, p, q); Quicksort(a, q + 1, r); // I'm pretty sure q + r was a typo, it doesn't work with q + r. } } ... it seems to be a correct sorting algorithm. I tested it out on a lot of random inputs, including all 0-1 arrays of length 20. I have also tried using this partition function for a selection algorithm, in which it failed to produce correct results. It seems to work and it's even very fast as part of the quicksort algorithm however. So my questions are: Can anyone post an example on which the algorithm DOESN'T work? If not, why does it work, since the partitioning part seems to be wrong? Is this another partitioning approach that I don't know about?

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• MySQL and INT auto_increment fields

  - by PHPguy

  Hello folks, I'm developing in LAMP (Linux+Apache+MySQL+PHP) since I remember myself. But one question was bugging me for years now. I hope you can help me to find an answer and point me into the right direction. Here is my challenge: Say, we are creating a community website, where we allow our users to register. The MySQL table where we store all users would look then like this: CREATE TABLE `users` ( `uid` int(2) unsigned NOT NULL auto_increment COMMENT 'User ID', `name` varchar(20) NOT NULL, `password` varchar(32) NOT NULL COMMENT 'Password is saved as a 32-bytes hash, never in plain text', `email` varchar(64) NOT NULL, `created` int(11) unsigned NOT NULL default '0' COMMENT 'Timestamp of registration', `updated` int(11) unsigned NOT NULL default '0' COMMENT 'Timestamp of profile update, e.g. change of email', PRIMARY KEY (`uid`) ) ENGINE=MyISAM DEFAULT CHARSET=utf8; So, from this snippet you can see that we have a unique and automatically incrementing for every new user 'uid' field. As on every good and loyal community website we need to provide users with possibility to completely delete their profile if they want to cancel their participation in our community. Here comes my problem. Let's say we have 3 registered users: Alice (uid = 1), Bob (uid = 2) and Chris (uid = 3). Now Bob want to delete his profile and stop using our community. If we delete Bob's profile from the 'users' table then his missing 'uid' will create a gap which will be never filled again. In my opinion it's a huge waste of uid's. I see 3 possible solutions here: 1) Increase the capacity of the 'uid' field in our table from SMALLINT (int(2)) to, for example, BIGINT (int(8)) and ignore the fact that some of the uid's will be wasted. 2) introduce the new field 'is_deleted', which will be used to mark deleted profiles (but keep them in the table, instead of deleting them) to re-utilize their uid's for newly registered users. The table will look then like this: CREATE TABLE `users` ( `uid` int(2) unsigned NOT NULL auto_increment COMMENT 'User ID', `name` varchar(20) NOT NULL, `password` varchar(32) NOT NULL COMMENT 'Password is saved as a 32-bytes hash, never in plain text', `email` varchar(64) NOT NULL, `is_deleted` int(1) unsigned NOT NULL default '0' COMMENT 'If equal to "1" then the profile has been deleted and will be re-used for new registrations', `created` int(11) unsigned NOT NULL default '0' COMMENT 'Timestamp of registration', `updated` int(11) unsigned NOT NULL default '0' COMMENT 'Timestamp of profile update, e.g. change of email', PRIMARY KEY (`uid`) ) ENGINE=MyISAM DEFAULT CHARSET=utf8; 3) Write a script to shift all following user records once a previous record has been deleted. E.g. in our case when Bob (uid = 2) decides to remove his profile, we would replace his record with the record of Chris (uid = 3), so that uid of Chris becomes qual to 2 and mark (is_deleted = '1') the old record of Chris as vacant for the new users. In this case we keep the chronological order of uid's according to the registration time, so that the older users have lower uid's. Please, advice me now which way is the right way to handle the gaps in the auto_increment fields. This is just one example with users, but such cases occur very often in my programming experience. Thanks in advance!

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• MVC design in Cocoa - are all 3 always necessary? Also: naming conventions, where to put Controller

  - by Nektarios

  I'm new to MVC although I've read a lot of papers and information on the web. I know it's somewhat ambiguous and there are many different interpretations of MVC patterns.. but the differences seem somewhat minimal My main question is - are M, V, and C always going to be necessary to be doing this right? I haven't seen anyone address this in anything I've read. Examples (I'm working in Cocoa/Obj-c although that shouldn't much matter).. 1) If I have a simple image on my GUI, or a text entry field that is just for a user's convenience and isn't saved or modified, these both would be V (view) but there's no M (no data and no domain processing going on), and no C to bridge them. So I just have some aspects that are "V" - seems fine 2) I have 2 different and visible windows that each have a button on them labeled as "ACTIVATE FOO" - when a user clicks the button on either, both buttons press in and change to say "DEACTIVATE FOO" and a third window appears with label "FOO". Clicking the button again will change the button on both windows to "ACTIVATE FOO" and will remove the third "FOO" window. In this case, my V consists of the buttons on both windows, and I guess also the third window (maybe all 3 windows). I definitely have a C, my Controller object will know about these buttons and windows and will get their clicks and hold generic states regarding windows and buttons. However, whether I have 1 button or 10 button, my window is called "FOO" or my window is called "BAR", this doesn't matter. There's no domain knowledge or data here - just control of views. So in this example, I really have "V" and "C" but no "M" - is that ok? 3) Final example, which I am running in to the most. I have a text entry field as my View. When I enter text in this, say a number representing gravity, I keep it in a Model that may do things like compute physics of a ball while taking in to account my gravity parameter. Here I have a V and an M, but I don't understand why I would need to add a C - a controller would just accept the signals from the View and pass it along to the Model, and vice versa. Being as the C is just a pure passthrough, it's really "junk" code and isn't making things any more reusable in my opinion. In most situations, when something changes I will need to change the C and M both in nearly identical ways. I realize it's probably an MVC beginner's mistake to think most situations call for only V and M.. leads me in to next subject 4) In Cocoa / Xcode / IB, I guess my Controllers should always be an instantiated object in IB? That is, I lay all of my "V" components in IB, and for each collection of View objects (things that are related) I should have an instantiated Controller? And then perhaps my Models should NOT be found in IB, and instead only found as classes in Xcode that tie in with Controller code found there. Is this accurate? This could explain why you'd have a Controller that is not really adding value - because you are keeping consistent.. 5) What about naming these things - for my above example about FOO / BAR maybe something that ends in Controller would be the C, like FancyWindowOpeningController, etc? And for models - should I suffix them with like GravityBallPhysicsModel etc, or should I just name those whatever I like? I haven't seen enough code to know what's out there in the wild and I want to get on the right track early on Thank you in advance for setting me straight or letting me know I'm on the right track. I feel like I'm starting to get it and most of what I say here makes sense, but validation of my guessing would help me feel confident..

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• Migrate Spring JPA DAO unit testing to google app engine

  - by twingocerise

  I'm trying to put together a simple environment where I can get Spring, Maven, JPA, Google App Engine and DAO unit testing working happily all together. The goal is to be able to run a simple DAO unit test creating an entity and then load it again with a simple find to check it's been created properly - all of this from my maven build. My dao is making use of the JPA entity manager (query(), persist(), etc.) I've got it working no problem with hsqldb and a datasource, etc. but I'm struggling to get it working with appengine. My questions are: 1) I'm using an entity manager, injecting my persistence unit as followed. Is it OK? Is there any need for a datasource or something special? I thought not but correct me if I'm wrong. applicationContext.xml <bean id='entityManagerFactory' class='org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean'> <property name="persistenceUnitName" value="transactions-optional" /> </bean> Persistence.xml <persistence-unit name="transactions-optional"> <provider>org.datanucleus.store.appengine.jpa.DatastorePersistenceProvider</provider> <properties> <property name="datanucleus.NontransactionalRead" value="true"/> <property name="datanucleus.NontransactionalWrite" value="true"/> <property name="datanucleus.ConnectionURL" value="appengine"/> </properties> </persistence-unit> 2) what are the dependencies I need to add to my pom file to be able to run the unit test making use of the entityManager? What about versions ? I found loads of things about appengine-api-labs/stubs/testing but none them got it working i.e. I'm getting jdo dependency missing while I'm using JPA... I also get loads of conflicts when I try to add some jars (datanucleus and stuff). So far I'm trying appengine-api-1.0-sdk v1.7.0 - ASM-all v3.3 - datanucleus core/api-jpa/enhancer v3.1.0 - datanucleus-appengine v2.0.1.1 and all the gae testing jars v1.7.0 3) Is there anything I need to add to my surefire plugin (test runner) to make sure it picks up all the dependencies? I'm getting an exhausting ClassNotFound on DatastorePersistenceProvider while it is in my classpath (I checked the jars and the mvn dependency:tree) I had a look at this but it doesn't seem to be working at all: http://www.vertigrated.com/blog/2011/02/working-maven-3-google-app-engine-plugin-with-gwt-support/ 4) Do I need to use any sot of localhelper to test my DAOs? Ideally I'd want to test my dao layer "as is" with the entity manager... what's your opinion ? Has anyone managed to run a unit test using JPA on google app engine ? 5) Do I need to set up any sort of gae.home somewhere in my pom file? Would anyone make use of it (a plugin or something) ? 6) Is the gwt-maven plugin any helpful if I don't use gwt - I'm writing a simple webservice making use of appengine, not a GWT app... Any help would be much appreciated as I've been struggling for 2 days now... Cheers, V.

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• CSS optimization - extra classes in dom or preprocessor-repetitive styling in css file?

  - by anna.mi

  I'm starting on a fairly large project and I'm considering the option of using LESS for pre-processing my css. the useful thing about LESS is that you can define a mixin that contains for example: .border-radius(@radius) { -webkit-border-radius: @radius; -moz-border-radius: @radius; -o-border-radius: @radius; -ms-border-radius: @radius; border-radius: @radius; } and then use it in a class declaration as .rounded-div { .border-radius(10px); } to get the outputted css as: .rounded-div { -webkit-border-radius: 10px; -moz-border-radius: 10px; -o-border-radius: 10px; -ms-border-radius: 10px; border-radius: 10px; } this is extremely useful in the case of browser prefixes. However this same concept could be used to encapsulate commonly-used css, for example: .column-container { overflow: hidden; display: block; width: 100%; } .column(@width) { float: left; width: @width; } and then use this mixin whenever i need columns in my design: .my-column-outer { .column-container(); background: red; } .my-column-inner { .column(50%); font-color: yellow; } (of course, using the preprocessor we could easily expand this to be much more useful, eg. pass the number of columns and the container width as variables and have LESS determine the width of each column depending on the number of columns and container width!) the problem with this is that when compliled, my final css file would have 100 such declarations, copy&pasted, making the file huge and bloated and repetitive. The alternative to this would be to use a grid system which has predefined classes for each column-layout option, eg .c-50 ( with a "float: left; width:50%;" definition ), .c-33, .c-25 to accomodate for a 2-column, 3-column and 4-column layout and then use these classes to my dom. i really mislike the idea of the extra classes, from experience it results to bloated dom (creating extra divs just to attach the grid classes to). Also the most basic tutorial for html/css would tell you that the dom should be separated from the styling - grid classes are styling related! to me, its the same as attaching a "border-radius-10" class to the .rounded-div example above! on the other hand, the large css file that would result from the repetitive code is also a disadvantage so i guess my question is, which one would you recommend? and which do you use? and, which solution is best for optimization? apart from the larger file size, has there even been any research on whether browser renders multiple classes faster than a large css file, or the other way round? tnx! i'd love to hear your opinion!

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• php array strip_tags and unset

  - by teo6389

  hello everybody i have a question regarding strip_tags function. i have an html document like that. <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"> <head> <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> <title>Untitled Document</title> </head> <body> <p>er</p> </body> </html> and this php script <?php $file = "ht.html"; $fp = fopen($file, "r"); $data = fread($fp, filesize($file)); fclose($fp); $output = str_replace("\t|\t", "|", $data); $outputline = explode("\n", $output); $lexeisline=count($outputline); for ($i = 0; $i < $lexeisline; $i++){ $outputline[$i]=strip_tags($outputline[$i]); if (empty($outputline[$i])){ unset($outputline[$i]); } } $outputline = array_values($outputline); $lexeisline=count($outputline); echo "<p>"; for ($i = 0; $i < $lexeisline; $i++){ echo ($outputline[$i])."<br />"; } echo "</p>"; ?> the problem is that it does not unset the empty vars(which are returned from the strip_tags) and echos something like this. does the following means that it echos empty strings? any opinion or help will be very appreciated. Thanx in advance <p> <br /> <br /> <br /> <br />Untitled Document <br /> <br /> <br />er <br /> <br /></p> @phpmeh Array ( [0] => [1] => [2] => [3] => [4] => Untitled Document [5] => [6] => [7] => er [8] => )

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• Dynamic JSON Parsing in .NET with JsonValue

  - by Rick Strahl

  So System.Json has been around for a while in Silverlight, but it's relatively new for the desktop .NET framework and now moving into the lime-light with the pending release of ASP.NET Web API which is bringing a ton of attention to server side JSON usage. The JsonValue, JsonObject and JsonArray objects are going to be pretty useful for Web API applications as they allow you dynamically create and parse JSON values without explicit .NET types to serialize from or into. But even more so I think JsonValue et al. are going to be very useful when consuming JSON APIs from various services. Yes I know C# is strongly typed, why in the world would you want to use dynamic values? So many times I've needed to retrieve a small morsel of information from a large service JSON response and rather than having to map the entire type structure of what that service returns, JsonValue actually allows me to cherry pick and only work with the values I'm interested in, without having to explicitly create everything up front. With JavaScriptSerializer or DataContractJsonSerializer you always need to have a strong type to de-serialize JSON data into. Wouldn't it be nice if no explicit type was required and you could just parse the JSON directly using a very easy to use object syntax? That's exactly what JsonValue, JsonObject and JsonArray accomplish using a JSON parser and some sweet use of dynamic sauce to make it easy to access in code. Creating JSON on the fly with JsonValue Let's start with creating JSON on the fly. It's super easy to create a dynamic object structure. JsonValue uses the dynamic  keyword extensively to make it intuitive to create object structures and turn them into JSON via dynamic object syntax. Here's an example of creating a music album structure with child songs using JsonValue:[TestMethod] public void JsonValueOutputTest() { // strong type instance var jsonObject = new JsonObject(); // dynamic expando instance you can add properties to dynamic album = jsonObject; album.AlbumName = "Dirty Deeds Done Dirt Cheap"; album.Artist = "AC/DC"; album.YearReleased = 1977; album.Songs = new JsonArray() as dynamic; dynamic song = new JsonObject(); song.SongName = "Dirty Deeds Done Dirt Cheap"; song.SongLength = "4:11"; album.Songs.Add(song); song = new JsonObject(); song.SongName = "Love at First Feel"; song.SongLength = "3:10"; album.Songs.Add(song); Console.WriteLine(album.ToString()); } This produces proper JSON just as you would expect: {"AlbumName":"Dirty Deeds Done Dirt Cheap","Artist":"AC\/DC","YearReleased":1977,"Songs":[{"SongName":"Dirty Deeds Done Dirt Cheap","SongLength":"4:11"},{"SongName":"Love at First Feel","SongLength":"3:10"}]} The important thing about this code is that there's no explicitly type that is used for holding the values to serialize to JSON. I am essentially creating this value structure on the fly by adding properties and then serialize it to JSON. This means this code can be entirely driven at runtime without compile time restraints of structure for the JSON output. Here I use JsonObject() to create a new object and immediately cast it to dynamic. JsonObject() is kind of similar in behavior to ExpandoObject in that it allows you to add properties by simply assigning to them. Internally, JsonValue/JsonObject these values are stored in pseudo collections of key value pairs that are exposed as properties through the DynamicObject functionality in .NET. The syntax gets a little tedious only if you need to create child objects or arrays that have to be explicitly defined first. Other than that the syntax looks like normal object access sytnax. Always remember though these values are dynamic - which means no Intellisense and no compiler type checking. It's up to you to ensure that the values you create are accessed consistently and without typos in your code. Note that you can also access the JsonValue instance directly and get access to the underlying type. This means you can assign properties by string, which can be useful for fully data driven JSON generation from other structures. Below you can see both styles of access next to each other:// strong type instance var jsonObject = new JsonObject(); // you can explicitly add values here jsonObject.Add("Entered", DateTime.Now); // expando style instance you can just 'use' properties dynamic album = jsonObject; album.AlbumName = "Dirty Deeds Done Dirt Cheap"; JsonValue internally stores properties keys and values in collections and you can iterate over them at runtime. You can also manipulate the collections if you need to to get the object structure to look exactly like you want. Again, if you've used ExpandoObject before JsonObject/Value are very similar in the behavior of the structure. Reading JSON strings into JsonValue The JsonValue structure supports importing JSON via the Parse() and Load() methods which can read JSON data from a string or various streams respectively. Essentially JsonValue includes the core JSON parsing to turn a JSON string into a collection of JsonValue objects that can be then referenced using familiar dynamic object syntax. Here's a simple example:[TestMethod] public void JsonValueParsingTest() { var jsonString = @"{""Name"":""Rick"",""Company"":""West Wind"",""Entered"":""2012-03-16T00:03:33.245-10:00""}"; dynamic json = JsonValue.Parse(jsonString); // values require casting string name = json.Name; string company = json.Company; DateTime entered = json.Entered; Assert.AreEqual(name, "Rick"); Assert.AreEqual(company, "West Wind"); } The JSON string represents an object with three properties which is parsed into a JsonValue object and cast to dynamic. Once cast to dynamic I can then go ahead and access the object using familiar object syntax. Note that the actual values - json.Name, json.Company, json.Entered - are actually of type JsonPrimitive and I have to assign them to their appropriate types first before I can do type comparisons. The dynamic properties will automatically cast to the right type expected as long as the compiler can resolve the type of the assignment or usage. The AreEqual() method oesn't as it expects two object instances and comparing json.Company to "West Wind" is comparing two different types (JsonPrimitive to String) which fails. So the intermediary assignment is required to make the test pass. The JSON structure can be much more complex than this simple example. Here's another example of an array of albums serialized to JSON and then parsed through with JsonValue():[TestMethod] public void JsonArrayParsingTest() { var jsonString = @"[ { ""Id"": ""b3ec4e5c"", ""AlbumName"": ""Dirty Deeds Done Dirt Cheap"", ""Artist"": ""AC/DC"", ""YearReleased"": 1977, ""Entered"": ""2012-03-16T00:13:12.2810521-10:00"", ""AlbumImageUrl"": ""http://ecx.images-amazon.com/images/I/61kTaH-uZBL._AA115_.jpg"", ""AmazonUrl"": ""http://www.amazon.com/gp/product/B00008BXJ4/ref=as_li_ss_tl?ie=UTF8&tag=westwindtechn-20&linkCode=as2&camp=1789&creative=390957&creativeASIN=B00008BXJ4"", ""Songs"": [ { ""AlbumId"": ""b3ec4e5c"", ""SongName"": ""Dirty Deeds Done Dirt Cheap"", ""SongLength"": ""4:11"" }, { ""AlbumId"": ""b3ec4e5c"", ""SongName"": ""Love at First Feel"", ""SongLength"": ""3:10"" }, { ""AlbumId"": ""b3ec4e5c"", ""SongName"": ""Big Balls"", ""SongLength"": ""2:38"" } ] }, { ""Id"": ""67280fb8"", ""AlbumName"": ""Echoes, Silence, Patience & Grace"", ""Artist"": ""Foo Fighters"", ""YearReleased"": 2007, ""Entered"": ""2012-03-16T00:13:12.2810521-10:00"", ""AlbumImageUrl"": ""http://ecx.images-amazon.com/images/I/41mtlesQPVL._SL500_AA280_.jpg"", ""AmazonUrl"": ""http://www.amazon.com/gp/product/B000UFAURI/ref=as_li_ss_tl?ie=UTF8&tag=westwindtechn-20&linkCode=as2&camp=1789&creative=390957&creativeASIN=B000UFAURI"", ""Songs"": [ { ""AlbumId"": ""67280fb8"", ""SongName"": ""The Pretender"", ""SongLength"": ""4:29"" }, { ""AlbumId"": ""67280fb8"", ""SongName"": ""Let it Die"", ""SongLength"": ""4:05"" }, { ""AlbumId"": ""67280fb8"", ""SongName"": ""Erase/Replay"", ""SongLength"": ""4:13"" } ] }, { ""Id"": ""7b919432"", ""AlbumName"": ""End of the Silence"", ""Artist"": ""Henry Rollins Band"", ""YearReleased"": 1992, ""Entered"": ""2012-03-16T00:13:12.2800521-10:00"", ""AlbumImageUrl"": ""http://ecx.images-amazon.com/images/I/51FO3rb1tuL._SL160_AA160_.jpg"", ""AmazonUrl"": ""http://www.amazon.com/End-Silence-Rollins-Band/dp/B0000040OX/ref=sr_1_5?ie=UTF8&qid=1302232195&sr=8-5"", ""Songs"": [ { ""AlbumId"": ""7b919432"", ""SongName"": ""Low Self Opinion"", ""SongLength"": ""5:24"" }, { ""AlbumId"": ""7b919432"", ""SongName"": ""Grip"", ""SongLength"": ""4:51"" } ] } ]"; dynamic albums = JsonValue.Parse(jsonString); foreach (dynamic album in albums) { Console.WriteLine(album.AlbumName + " (" + album.YearReleased.ToString() + ")"); foreach (dynamic song in album.Songs) { Console.WriteLine("\t" + song.SongName ); } } Console.WriteLine(albums[0].AlbumName); Console.WriteLine(albums[0].Songs[1].SongName);}   It's pretty sweet how easy it becomes to parse even complex JSON and then just run through the object using object syntax, yet without an explicit type in the mix. In fact it looks and feels a lot like if you were using JavaScript to parse through this data, doesn't it? And that's the point…© Rick Strahl, West Wind Technologies, 2005-2012Posted in .NET  Web Api  JSON   Tweet !function(d,s,id){var js,fjs=d.getElementsByTagName(s)[0];if(!d.getElementById(id)){js=d.createElement(s);js.id=id;js.src="//platform.twitter.com/widgets.js";fjs.parentNode.insertBefore(js,fjs);}}(document,"script","twitter-wjs"); (function() { var po = document.createElement('script'); po.type = 'text/javascript'; po.async = true; po.src = 'https://apis.google.com/js/plusone.js'; var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(po, s); })();

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• Mauritius Software Craftsmanship Community

  There we go! I finally managed to push myself forward and pick up an old, actually too old, idea since I ever arrived here in Mauritius more than six years ago. I'm talking about a community for all kind of ICT connected people. In the past (back in Germany), I used to be involved in various community activities. For example, I was part of the Microsoft Community Leader/Influencer Program (CLIP) in Germany due to an FAQ on Visual FoxPro, actually Active FoxPro Pages (AFP) to be more precise. Then in 2003/2004 I addressed the responsible person of the dFPUG user group in Speyer in order to assist him in organising monthly user group meetings. Well, he handed over management completely, and attended our meetings regularly. Why did it take you so long? Well, I don't want to bother you with the details but short version is that I was too busy on either job (building up new companies) or private life (got married and we have two lovely children, eh 'monsters') or even both. But now is the time where I was starting to look for new fields given the fact that I gained some spare time. My businesses are up and running, the kids are in school, and I am finally in a position where I can commit myself again to community activities. And I love to do that! Why a new user group? Good question... And 'easy' to answer. Since back in 2007 I did my usual research, eh Google searches, to see whether there existing user groups in Mauritius and in which field of interest. And yes, there are! If I recall this correctly, then there are communities for PHP, Drupal, Python (just recently), Oracle, and Linux (which used to be even two). But... either they do not exist anymore, they are dormant, or there is only a low heart-beat, frankly speaking. And yes, I went to meetings of the Linux User Group Meta (Mauritius) back in 2010/2011 and just recently. I really like the setup and the way the LUGM is organised. It's just that I have a slightly different point of view on how a user group or community should organise itself and how to approach future members. Don't get me wrong, I'm not criticizing others doing a very good job, I'm only saying that I'd like to do it differently. The last meeting of the LUGM was awesome; read my feedback about it. Ok, so what's up with 'Mauritius Software Craftsmanship Community' or short: MSCC? As I've already written in my article on 'Communities - The importance of exchange and discussion' I think it is essential in a world of IT to stay 'connected' with a good number of other people in the same field. There is so much dynamic and every day's news that it is almost impossible to keep on track with all of them. The MSCC is going to provide a common platform to exchange experience and share knowledge between each other. You might be a newbie and want to know what to expect working as a software developer, or as a database administrator, or maybe as an IT systems administrator, or you're an experienced geek that loves to share your ideas or solutions that you implemented to solve a specific problem, or you're the business (or HR) guy that is looking for 'fresh' blood to enforce your existing team. Or... you're just interested and you'd like to communicate with like-minded people. Meetup of 26.06.2013 @ L'arabica: Of course there are laptops around. Free WiFi, power outlet, coffee, code and Linux in one go. The MSCC is technology-agnostic and spans an umbrella over any kind of technology. Simply because you can't ignore other technologies anymore in a connected IT world as we have. A front-end developer for iOS applications should have the chance to connect with a Python back-end coder and eventually with a DBA for MySQL or PostgreSQL and exchange their experience. Furthermore, I'm a huge fan of cross-platform development, and it is very pleasant to have pure Web developers - with all that HTML5, CSS3, JavaScript and JS libraries stuff - and passionate C# or Java coders at the same table. This diversity of knowledge can assist and boost your personal situation. And last but not least, there are projects and open positions 'flying' around... People might like to hear others opinion about an employer or get new impulses on how to tackle down an issue at their workspace, etc. This is about community. And that's how I see the MSCC in general - free of any limitations be it by programming language or technology. Having the chance to exchange experience and to discuss certain aspects of technology saves you time and money, and it's a pleasure to enjoy. Compared to dusty books and remote online resources. It's human! Organising meetups (meetings, get-together, gatherings - you name it!) As of writing this article, the MSCC is currently meeting every Wednesday for the weekly 'Code & Coffee' session at various locations (suggestions are welcome!) in Mauritius. This might change in the future eventually but especially at the beginning I think it is very important to create awareness in the Mauritian IT world. Yes, we are here! Come and join us! ;-) The MSCC's main online presence is located at Meetup.com because it allows me to handle the organisation of events and meeting appointments very easily, and any member can have a look who else is involved so that an exchange of contacts is given at any time. In combination with the other entities (G+ Communities, FB Pages or in Groups) I advertise and manage all future activities here: Mauritius Software Craftsmanship Community This is a community for those who care and are proud of what they do. For those developers, regardless how experienced they are, who want to improve and master their craft. This is a community for those who believe that being average is just not good enough. I know, there are not many 'craftsmen' yet but it's a start... Let's see how it looks like by the end of the year. There are free smartphone apps for Android and iOS from Meetup.com that allow you to keep track of meetings and to stay informed on latest updates. And last but not least, there is a Trello workspace to collect and share ideas and provide downloads of slides, etc. Trello is also available as free smartphone app. Sharing is caring! As mentioned, the #MSCC is present in various social media networks in order to cover as many people as possible here in Mauritius. Following is an overview of the current networks: Twitter - Latest updates and quickies Google+ - Community channel Facebook - Community Page LinkedIn - Community Group Trello - Collaboration workspace to share and develop ideas Hopefully, this covers the majority of computer-related people in Mauritius. Please spread the word about the #MSCC between your colleagues, your friends and other interested 'geeks'. Your future looks bright Running and participating in a user group or any kind of community usually provides quite a number of advantages for anyone. On the one side it is very joyful for me to organise appointments and get in touch with people that might be interested to present a little demo of their projects or their recent problems they had to tackle down, and on the other side there are lots of companies that have various support programs or sponsorships especially tailored for user groups. At the moment, I already have a couple of gimmicks that I would like to hand out in small contests or raffles during one of the upcoming meetings, and as said, companies provide all kind of goodies, books free of charge, or sometimes even licenses for communities. Meeting other software developers or IT guys also opens up your point of view on the local market and there might be interesting projects or job offers available, too. A community like the Mauritius Software Craftsmanship Community is great for freelancers, self-employed, students and of course employees. Meetings will be organised on a regular basis, and I'm open to all kind of suggestions from you. Please leave a comment here in blog or join the conversations in the above mentioned social networks. Let's get this community up and running, my fellow Mauritians! Recent updates The MSCC is now officially participating in the O'Reilly UK User Group programm and we are allowed to request review or recension copies of recent titles. Additionally, we have a discount code for any books or ebooks that you might like to order on shop.oreilly.com. More applications for user group sponsorship programms are pending and I'm looking forward to a couple of announcement very soon. And... we need some kind of 'corporate identity' - Over at the MSCC website there is a call for action (or better said a contest with prizes) to create a unique design for the MSCC. This would include a decent colour palette, a logo, graphical banners for Meetup, Google+, Facebook, LinkedIn, etc. and of course badges for our craftsmen to add to their personal blogs and websites. Please spread the word and contribute. Thanks!

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• Pluralsight Meet the Author Podcast on Structuring JavaScript Code

  - by dwahlin

  I had the opportunity to talk with Fritz Onion from Pluralsight about one of my recent courses titled Structuring JavaScript Code for one of their Meet the Author podcasts. We talked about why JavaScript patterns are important for building more re-useable and maintainable apps, pros and cons of different patterns, and how to go about picking a pattern as a project is started. The course provides a solid walk-through of converting what I call “Function Spaghetti Code” into more modular code that’s easier to maintain, more re-useable, and less susceptible to naming conflicts. Patterns covered in the course include the Prototype Pattern, Revealing Module Pattern, and Revealing Prototype Pattern along with several other tips and techniques that can be used. Meet the Author:  Dan Wahlin on Structuring JavaScript Code   The transcript from the podcast is shown below: [Fritz]  Hello, this is Fritz Onion with another Pluralsight author interview. Today we’re talking with Dan Wahlin about his new course, Structuring JavaScript Code. Hi, Dan, it’s good to have you with us today. [Dan]  Thanks for having me, Fritz. [Fritz]  So, Dan, your new course, which came out in December of 2011 called Structuring JavaScript Code, goes into several patterns of usage in JavaScript as well as ways of organizing your code and what struck me about it was all the different techniques you described for encapsulating your code. I was wondering if you could give us just a little insight into what your motivation was for creating this course and sort of why you decided to write it and record it. [Dan]  Sure. So, I got started with JavaScript back in the mid 90s. In fact, back in the days when browsers that most people haven’t heard of were out and we had JavaScript but it wasn’t great. I was on a project in the late 90s that was heavy, heavy JavaScript and we pretty much did what I call in the course function spaghetti code where you just have function after function, there’s no rhyme or reason to how those functions are structured, they just kind of flow and it’s a little bit hard to do maintenance on it, you really don’t get a lot of reuse as far as from an object perspective. And so coming from an object-oriented background in JAVA and C#, I wanted to put something together that highlighted kind of the new way if you will of writing JavaScript because most people start out just writing functions and there’s nothing with that, it works, but it’s definitely not a real reusable solution. So the course is really all about how to move from just kind of function after function after function to the world of more encapsulated code and more reusable and hopefully better maintenance in the process. [Fritz]  So I am sure a lot of people have had similar experiences with their JavaScript code and will be looking forward to seeing what types of patterns you’ve put forth. Now, a couple I noticed in your course one is you start off with the prototype pattern. Do you want to describe sort of what problem that solves and how you go about using it within JavaScript? [Dan]  Sure. So, the patterns that are covered such as the prototype pattern and the revealing module pattern just as two examples, you know, show these kind of three things that I harp on throughout the course of encapsulation, better maintenance, reuse, those types of things. The prototype pattern specifically though has a couple kind of pros over some of the other patterns and that is the ability to extend your code without touching source code and what I mean by that is let’s say you’re writing a library that you know either other teammates or other people just out there on the Internet in general are going to be using. With the prototype pattern, you can actually write your code in such a way that we’re leveraging the JavaScript property and by doing that now you can extend my code that I wrote without touching my source code script or you can even override my code and perform some new functionality. Again, without touching my code.  And so you get kind of the benefit of the almost like inheritance or overriding in object oriented languages with this prototype pattern and it makes it kind of attractive that way definitely from a maintenance standpoint because, you know, you don’t want to modify a script I wrote because I might roll out version 2 and now you’d have to track where you change things and it gets a little tricky. So with this you just override those pieces or extend them and get that functionality and that’s kind of some of the benefits that that pattern offers out of the box. [Fritz]  And then the revealing module pattern, how does that differ from the prototype pattern and what problem does that solve differently? [Dan]  Yeah, so the prototype pattern and there’s another one that’s kind of really closely lined with revealing module pattern called the revealing prototype pattern and it also uses the prototype key word but it’s very similar to the one you just asked about the revealing module pattern. [Fritz]  Okay. [Dan]  This is a really popular one out there. In fact, we did a project for Microsoft that was very, very heavy JavaScript. It was an HMTL5 jQuery type app and we use this pattern for most of the structure if you will for the JavaScript code and what it does in a nutshell is allows you to get that encapsulation so you have really a single function wrapper that wraps all your other child functions but it gives you the ability to do public versus private members and this is kind of a sort of debate out there on the web. Some people feel that all JavaScript code should just be directly accessible and others kind of like to be able to hide their, truly their private stuff and a lot of people do that. You just put an underscore in front of your field or your variable name or your function name and that kind of is the defacto way to say hey, this is private. With the revealing module pattern you can do the equivalent of what objective oriented languages do and actually have private members that you literally can’t get to as an external consumer of the JavaScript code and then you can expose only those members that you want to be public. Now, you don’t get the benefit though of the prototype feature, which is I can’t easily extend the revealing module pattern type code if you don’t like something I’m doing, chances are you’re probably going to have to tweak my code to fix that because we’re not leveraging prototyping but in situations where you’re writing apps that are very specific to a given target app, you know, it’s not a library, it’s not going to be used in other apps all over the place, it’s a pattern I actually like a lot, it’s very simple to get going and then if you do like that public/private feature, it’s available to you. [Fritz]  Yeah, that’s interesting. So it’s almost, you can either go private by convention just by using a standard naming convention or you can actually enforce it by using the prototype pattern. [Dan]  Yeah, that’s exactly right. [Fritz]  So one of the things that I know I run across in JavaScript and I’m curious to get your take on is we do have all these different techniques of encapsulation and each one is really quite different when you’re using closures versus simply, you know, referencing member variables and adding them to your objects that the syntax changes with each pattern and the usage changes. So what would you recommend for people starting out in a brand new JavaScript project? Should they all sort of decide beforehand on what patterns they’re going to stick to or do you change it based on what part of the library you’re working on? I know that’s one of the points of confusion in this space. [Dan]  Yeah, it’s a great question. In fact, I just had a company ask me about that. So which one do I pick and, of course, there’s not one answer fits all. [Fritz]  Right. [Dan]  So it really depends what you just said is absolutely in my opinion correct, which is I think as a, especially if you’re on a team or even if you’re just an individual a team of one, you should go through and pick out which pattern for this particular project you think is best. Now if it were me, here’s kind of the way I think of it. If I were writing a let’s say base library that several web apps are going to use or even one, but I know that there’s going to be some pieces that I’m not really sure on right now as I’m writing I and I know people might want to hook in that and have some better extension points, then I would look at either the prototype pattern or the revealing prototype. Now, really just a real quick summation between the two the revealing prototype also gives you that public/private stuff like the revealing module pattern does whereas the prototype pattern does not but both of the prototype patterns do give you the benefit of that extension or that hook capability. So, if I were writing a library that I need people to override things or I’m not even sure what I need them to override, I want them to have that option, I’d probably pick a prototype, one of the prototype patterns. If I’m writing some code that is very unique to the app and it’s kind of a one off for this app which is what I think a lot of people are kind of in that mode as writing custom apps for customers, then my personal preference is the revealing module pattern you could always go with the module pattern as well which is very close but I think the revealing module patterns a little bit cleaner and we go through that in the course and explain kind of the syntax there and the differences. [Fritz]  Great, that makes a lot of sense. [Fritz]  I appreciate you taking the time, Dan, and I hope everyone takes a chance to look at your course and sort of make these decisions for themselves in their next JavaScript project. Dan’s course is, Structuring JavaScript Code and it’s available now in the Pluralsight Library. So, thank you very much, Dan. [Dan]  Thanks for having me again.

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• Adventures in MVVM &ndash; My ViewModel Base

  - by Brian Genisio's House Of Bilz

  More Adventures in MVVM First, I’d like to say: THIS IS NOT A NEW MVVM FRAMEWORK. I tend to believe that MVVM support code should be specific to the system you are building and the developers working on it.  I have yet to find an MVVM framework that does everything I want it to without doing too much.  Don’t get me wrong… there are some good frameworks out there.  I just like to pick and choose things that make sense for me.  I’d also like to add that some of these features only work in WPF.  As of Silveright 4, they don’t support binding to dynamic properties, so some of the capabilities are lost. That being said, I want to share my ViewModel base class with the world.  I have had several conversations with people about the problems I have solved using this ViewModel base.  A while back, I posted an article about some experiments with a “Rails Inspired ViewModel”.  What followed from those ideas was a ViewModel base class that I take with me and use in my projects.  It has a lot of features, all designed to reduce the friction in writing view models. I have put the code out on Codeplex under the project: ViewModelSupport. Finally, this article focuses on the ViewModel and only glosses over the View and the Model.  Without all three, you don’t have MVVM.  But this base class is for the ViewModel, so that is what I am focusing on. Features: Automatic Command Plumbing Property Change Notification Strongly Typed Property Getter/Setters Dynamic Properties Default Property values Derived Properties Automatic Method Execution Command CanExecute Change Notification Design-Time Detection What about Silverlight? Automatic Command Plumbing This feature takes the plumbing out of creating commands.  The common pattern for commands in a ViewModel is to have an Execute method as well as an optional CanExecute method.  To plumb that together, you create an ICommand Property, and set it in the constructor like so: Before public class AutomaticCommandViewModel { public AutomaticCommandViewModel() { MyCommand = new DelegateCommand(Execute_MyCommand, CanExecute_MyCommand); } public void Execute_MyCommand() { // Do something } public bool CanExecute_MyCommand() { // Are we in a state to do something? return true; } public DelegateCommand MyCommand { get; private set; } } With the base class, this plumbing is automatic and the property (MyCommand of type ICommand) is created for you.  The base class uses the convention that methods be prefixed with Execute_ and CanExecute_ in order to be plumbed into commands with the property name after the prefix.  You are left to be expressive with your behavior without the plumbing.  If you are wondering how CanExecuteChanged is raised, see the later section “Command CanExecute Change Notification”. After public class AutomaticCommandViewModel : ViewModelBase { public void Execute_MyCommand() { // Do something } public bool CanExecute_MyCommand() { // Are we in a state to do something? return true; } }   Property Change Notification One thing that always kills me when implementing ViewModels is how to make properties that notify when they change (via the INotifyPropertyChanged interface).  There have been many attempts to make this more automatic.  My base class includes one option.  There are others, but I feel like this works best for me. The common pattern (without my base class) is to create a private backing store for the variable and specify a getter that returns the private field.  The setter will set the private field and fire an event that notifies the change, only if the value has changed. Before public class PropertyHelpersViewModel : INotifyPropertyChanged { private string text; public string Text { get { return text; } set { if(text != value) { text = value; RaisePropertyChanged("Text"); } } } protected void RaisePropertyChanged(string propertyName) { var handlers = PropertyChanged; if(handlers != null) handlers(this, new PropertyChangedEventArgs(propertyName)); } public event PropertyChangedEventHandler PropertyChanged; } This way of defining properties is error-prone and tedious.  Too much plumbing.  My base class eliminates much of that plumbing with the same functionality: After public class PropertyHelpersViewModel : ViewModelBase { public string Text { get { return Get<string>("Text"); } set { Set("Text", value);} } }   Strongly Typed Property Getters/Setters It turns out that we can do better than that.  We are using a strongly typed language where the use of “Magic Strings” is often frowned upon.  Lets make the names in the getters and setters strongly typed: A refinement public class PropertyHelpersViewModel : ViewModelBase { public string Text { get { return Get(() => Text); } set { Set(() => Text, value); } } }   Dynamic Properties In C# 4.0, we have the ability to program statically OR dynamically.  This base class lets us leverage the powerful dynamic capabilities in our ecosystem. (This is how the automatic commands are implemented, BTW)  By calling Set(“Foo”, 1), you have now created a dynamic property called Foo.  It can be bound against like any static property.  The opportunities are endless.  One great way to exploit this behavior is if you have a customizable view engine with templates that bind to properties defined by the user.  The base class just needs to create the dynamic properties at runtime from information in the model, and the custom template can bind even though the static properties do not exist. All dynamic properties still benefit from the notifiable capabilities that static properties do. For any nay-sayers out there that don’t like using the dynamic features of C#, just remember this: the act of binding the View to a ViewModel is dynamic already.  Why not exploit it?  Get over it :) Just declare the property dynamically public class DynamicPropertyViewModel : ViewModelBase { public DynamicPropertyViewModel() { Set("Foo", "Bar"); } } Then reference it normally <TextBlock Text="{Binding Foo}" />   Default Property Values The Get() method also allows for default properties to be set.  Don’t set them in the constructor.  Set them in the property and keep the related code together: public string Text { get { return Get(() => Text, "This is the default value"); } set { Set(() => Text, value);} }   Derived Properties This is something I blogged about a while back in more detail.  This feature came from the chaining of property notifications when one property affects the results of another, like this: Before public class DependantPropertiesViewModel : ViewModelBase { public double Score { get { return Get(() => Score); } set { Set(() => Score, value); RaisePropertyChanged("Percentage"); RaisePropertyChanged("Output"); } } public int Percentage { get { return (int)(100 * Score); } } public string Output { get { return "You scored " + Percentage + "%."; } } } The problem is: The setter for Score has to be responsible for notifying the world that Percentage and Output have also changed.  This, to me, is backwards.    It certainly violates the “Single Responsibility Principle.” I have been bitten in the rear more than once by problems created from code like this.  What we really want to do is invert the dependency.  Let the Percentage property declare that it changes when the Score Property changes. After public class DependantPropertiesViewModel : ViewModelBase { public double Score { get { return Get(() => Score); } set { Set(() => Score, value); } } [DependsUpon("Score")] public int Percentage { get { return (int)(100 * Score); } } [DependsUpon("Percentage")] public string Output { get { return "You scored " + Percentage + "%."; } } }   Automatic Method Execution This one is extremely similar to the previous, but it deals with method execution as opposed to property.  When you want to execute a method triggered by property changes, let the method declare the dependency instead of the other way around. Before public class DependantMethodsViewModel : ViewModelBase { public double Score { get { return Get(() => Score); } set { Set(() => Score, value); WhenScoreChanges(); } } public void WhenScoreChanges() { // Handle this case } } After public class DependantMethodsViewModel : ViewModelBase { public double Score { get { return Get(() => Score); } set { Set(() => Score, value); } } [DependsUpon("Score")] public void WhenScoreChanges() { // Handle this case } }   Command CanExecute Change Notification Back to Commands.  One of the responsibilities of commands that implement ICommand – it must fire an event declaring that CanExecute() needs to be re-evaluated.  I wanted to wait until we got past a few concepts before explaining this behavior.  You can use the same mechanism here to fire off the change.  In the CanExecute_ method, declare the property that it depends upon.  When that property changes, the command will fire a CanExecuteChanged event, telling the View to re-evaluate the state of the command.  The View will make appropriate adjustments, like disabling the button. DependsUpon works on CanExecute methods as well public class CanExecuteViewModel : ViewModelBase { public void Execute_MakeLower() { Output = Input.ToLower(); } [DependsUpon("Input")] public bool CanExecute_MakeLower() { return !string.IsNullOrWhiteSpace(Input); } public string Input { get { return Get(() => Input); } set { Set(() => Input, value);} } public string Output { get { return Get(() => Output); } set { Set(() => Output, value); } } }   Design-Time Detection If you want to add design-time data to your ViewModel, the base class has a property that lets you ask if you are in the designer.  You can then set some default values that let your designer see what things might look like in runtime. Use the IsInDesignMode property public DependantPropertiesViewModel() { if(IsInDesignMode) { Score = .5; } }   What About Silverlight? Some of the features in this base class only work in WPF.  As of version 4, Silverlight does not support binding to dynamic properties.  This, in my opinion, is a HUGE limitation.  Not only does it keep you from using many of the features in this ViewModel, it also keeps you from binding to ViewModels designed in IronRuby.  Does this mean that the base class will not work in Silverlight?  No.  Many of the features outlined in this article WILL work.  All of the property abstractions are functional, as long as you refer to them statically in the View.  This, of course, means that the automatic command hook-up doesn’t work in Silverlight.  You need to plumb it to a static property in order for the Silverlight View to bind to it.  Can I has a dynamic property in SL5?     Good to go? So, that concludes the feature explanation of my ViewModel base class.  Feel free to take it, fork it, whatever.  It is hosted on CodePlex.  When I find other useful additions, I will add them to the public repository.  I use this base class every day.  It is mature, and well tested.  If, however, you find any problems with it, please let me know!  Also, feel free to suggest patches to me via the CodePlex site.  :)

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