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• Practical rules for premature optimization

  - by DougW

  It seems that the phrase "Premature Optimization" is the buzz-word of the day. For some reason, iphone programmers in particular seem to think of avoiding premature optimization as a pro-active goal, rather than the natural result of simply avoiding distraction. The problem is, the term is beginning to be applied more and more to cases that are completely inappropriate. For example, I've seen a growing number of people say not to worry about the complexity of an algorithm, because that's premature optimization (eg http://stackoverflow.com/questions/2190275/help-sorting-an-nsarray-across-two-properties-with-nssortdescriptor/2191720#2191720). Frankly, I think this is just laziness, and appalling to disciplined computer science. But it has occurred to me that maybe considering the complexity and performance of algorithms is going the way of assembly loop unrolling, and other optimization techniques that are now considered unnecessary. What do you think? Are we at the point now where deciding between an O(n^n) and O(n!) complexity algorithm is irrelevant? What about O(n) vs O(n*n)? What do you consider "premature optimization"? What practical rules do you use to consciously or unconsciously avoid it? This is a bit vague, but I'm curious to hear other peoples' opinions on the topic.

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• Nested namespaces, correct static library design issues

  - by PeterK

  Hello all, I'm currently in the process of developing a fairly large static library which will be used by some tools when it's finished. Now since this project is somewhat larger than anything i've been involved in so far, I realized its time to think of a good structure for the project. Using namespaces is one of those logical steps. My current approach is to divide the library into parts (which are not standalone, but their purpose calls for such a separation). I have a 'core' part which now just holds some very common typedefs and constants (used by many different parts of the library). Other parts are for example some 'utils' (hash etc.), file i/o and so on. Each of these parts has its own namespace. I have nearly finished the 'utils' part and realized that my approach probably is not the best. The problem (if we want to call it so) is that in the 'utils' namespace i need something from the 'core' namespace which results in including the core header files and many using directives. So i began to think that this probably is not a good thing and should be changed somehow. My first idea is to use nested namespaces as to have something like core::utils. Since this will require some heavy refactoring i want to ask here first. What do you think? How would you handle this? Or more generally: How to correctly design a static library in terms of namespaces and code organization? If there are some guidelines or articles about it, please mentoin them too. Thanks. Note: i'm quite sure that there are more good approaches than just one. Feel free to post your ideas, suggestions etc. Since i'm designing this library i want it to be really good. The goal is to make it as clean and FAST as possible. The only problem is that i will have to integrate a LOT of existing code and refactor it, which will really be a painful process (sigh) - thats why good structure is so important)

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• .Net System.Mail.Message adding multiple "To" addresses

  - by Matt Dawdy

  I just hit something I think is inconsistent, and wanted to see if I'm doing something wrong, if I'm an idiot, or... MailMessage msg = new MailMessage(); msg.To.Add("[email protected]"); msg.To.Add("[email protected]"); msg.To.Add("[email protected]"); msg.To.Add("[email protected]"); Really only sends this email to 1 person, the last one. To add multiples I have to do this: msg.To.Add("[email protected],[email protected],[email protected],[email protected]"); I don't get it. I thought I was adding multiple people to the "To" address collection, but what I was doing was replacing it. I think I just realized my error -- to add one item to the collection, use .To.Add(new MailAddress("[email protected]")) If you use just a string, it replaces everything it had in its list. Ugh. I'd consider this a rather large gotcha! Since I answered my own question, but I think this is of value to have in the stackoverflow archive, I'll still ask it. Maybe someone even has an idea of other traps that you can fall into.

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• Rails running multiple delayed_job - lock tables

  - by pepernik

  Hey. I use delayed_job for background processing. I have 8 CPU server, MySQL and I start 7 delayed_job processes RAILS_ENV=production script/delayed_job -n 7 start Q1: I'm wondering is it possible that 2 or more delayed_job processes start processing the same process (the same record-row in the database delayed_jobs). I checked the code of the delayed_job plugin but can not find the lock directive in a way it should be. I think each process should lock the database table before executing an UPDATE on lock_by column. They lock the record simply by updating the locked_by field (UPDATE delayed_jobs SET locked_by...). Is that really enough? No locking needed? Why? I know that UPDATE has higher priority than SELECT but I think this does not have the effect in this case. My understanding of the multy-threaded situation is: Process1: Get waiting job X. [OK] Process2: Get waiting jobs X. [OK] Process1: Update locked_by field. [OK] Process2: Update locked_by field. [OK] Process1: Get waiting job X. [Already processed] Process2: Get waiting jobs X. [Already processed] I think in some cases more jobs can get the same information and can start processing the same process. Q2: Is 7 delayed_jobs a good number for 8CPU server? Why yes/not. Thx 10x!

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• are projects with high developer turn over rate really a bad thing?

  - by John

  I've inherited a lot of web projects that experienced high developer turn over rates. Sometimes these web projects are a horrible patchwork of band aid solutions. Other times they can be somewhat maintainable mozaics of half-done features each built with a different architectural style. Everytime I inherit these projects, I wish the previous developers could explain to me why things got so bad. What puzzles me is the reaction of the owners (either a manager, a middle man company, or a client). They seem to think, "Well, if you leave, I'll just find another developer." Or they think, "Oh, it costs that much money to refactor the system? I know another developer who can do it at half the price. I'll hire him if I can't afford you." I'm guessing that the high developer turn over rate is related to the owner's mentality of "If you think it's a bad idea to build this, I'll just find another (possibly cheaper) developer to do what I want". For the owners, the approach seems to work because their business is thriving. Unfortunately, it's no fun for the developers that go AWOL 3-4 months after working with poor code, strict timelines, and little feedback. So my question is the following: Are the following symptoms of a project really such a bad thing for business? high developer turn over rate poorly built technology - often a patchwork of different and inappropriately used architectural styles owners without a clear roadmap for their web project, and they request features on a whim I've seen numerous businesses prosper while experiencing the symptoms above. So as a programmer, even though my instincts tell me the above points are terrible, I'm forced to take a step back and ask, "are things really that bad in the grand scheme of things?" If not, I will re-evaluate my approach to these projects.

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• pluto or jetspeed on google app engine?

  - by Patrick Cornelissen

  I am trying to build something "portlet server"-ish on the google app engine. (as open source) I'd like to use the JSR168/286 standards, but I think that the restrictions of the app engine will make it somewhere between tricky and impossible. Has anyone tried to run jetspeed or an application that uses pluto internally on the google app engine? Based on my current knowledge of portlets and the google app engine I'm anticipating these problems: A war file with portlets is from the deployment standpoint more or less a complete webapp (yes, I know that it doesn't really work without a portal server). The war file may contain it's own web.xml etc. This makes deployment on the app engine rather difficult, because the apps are not visible to each other, so all portlet containing archives need to be included in the war file of the deployed "app engine based portal server". The "portlets" are (at least in liferay) started as permanent servlet processes, based on their portlet.xmls and web.xmls which is located in the same spot for every portlet archive that is loaded. I think this may be problematic in the app engine, because everything is in one big "web app", so it may be tricky to access the portlet.xmls from each archive. This prevents a 100% compatibility in my opinion. Is here anyone who has any experience with the combination of portlets and the app engine? Do you think it's feasible to modify jetspeed, pluto or any other portlet container to be able to run it on the app engine?

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• how would you like computer science classes to be taught?

  - by aaa

  hello I am a graduate student now, and hopefully someday I will teach. my interests are C++, Python, embedded languages, and scientific computing. Meanwhile I daydream about how I would teach. I was not quite happy with my undergraduate university as I found many computer science classes lacking. so I would like to ask you, if you were a student, how would you like your computer science classes to be taught? I understand it is a very subjective question, but nevertheless I think it's important to know what people want. Some specific points I am interested in: should computer languages be taught explicitly, or should students be required to pick up language on their own? what is better for learning, tests, projects, some sort of take-home exam? how do you think classtime should be used? theory, introduction, explanations, etc.? do you think the group projects are important? how much about computer architecture do you want to learn in computer science class, not necessarily assembler class. should particular operating system/editor be mandated or encouraged? Thanks thank you for your comments. Question has been closed because it is a discussion question rather than Q&A. If you know appropriate website for discussions of such sort with low noise ratio, please let me know.

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• Using file() incrementally?

  - by NeedBeerStat

  I'm not sure if this is possible, I've been googling for a solution... But, essentially, I have a very large file, the lines of which I want to store in an array. Thus, I'm using file(), but is there a way to do that in batches? So that every,say, 100 lines it creates, it "pauses"? I think there's likely to be something I can do with a foreach loop or something, but I'm not sure that I'm thinking about it the right way... Like $i=0; $j=0; $throttle=100; foreach($files as $k => $v) { if($i < $j+$throttle && $i > $j) { $lines[] = file($v); //Do some other stuff, like importing into a db } $i++; $j++; } But, I think that won't really work because $i & $j will always be equal... Anyway, feeling muddled... Can someone help me think a lil' clearer?

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• Interface vs Abstract Class (general OO)

  - by Kave

  Hi, I have had recently two telephone interviews where I've been asked about the differences between an Interface and an Abstract class. I have explained every aspect of them I could think of, but it seems they are waiting for me to mention something specific, and I dont know what it is. From my experience I think the following is true, if i am missing a major point please let me know: Interface: Every single Method declared in an Interface will have to be implemented in the subclass. Only Events, Delegates, Properties (C#) and Methods can exist in a Interface. A class can implement multiple Interfaces. Abstract Class Only Abstract methods have to be implemented by the subclass. An Abstract class can have normal methods with implementations. Abstract class can also have class variables beside Events, Delegates, Properties and Methods. A class can only implement one abstract class only due non-existence of Multi-inheritance in C#. 1) After all that the interviewer came up with the question What if you had an Abstract class with only abstract methods, how would that be different from an interface? I didnt know the answer but I think its the inheritance as mentioned above right? 2) An another interviewer asked me what if you had a Public variable inside the interface, how would that be different than in Abstract Class? I insisted you can't have a public variable inside an interface. I didn't know what he wanted to hear but he wasn't satisfied either. Many Thanks for clarification, Kave See Also: When to use an interface instead of an abstract class and vice versa Interfaces vs. Abstract Classes How do you decide between using an Abstract Class and an Interface?

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• PHP: Profiling code and strict environment ~ Improving my coding

  - by DavidYell

  I would like to update my local working environment to be stricter in an effort to improve my code. I know that my code is okay, but as with most things there is always room for improvement. I use XAMPP on my local machine, for simplicities sake Apache Friends XAMPP (Basic Package) version 1.7.2 So I've updated my php.ini : error_reporting to be E_ALL | E_STRICT to help with the code standard. I've also enabled the XDebug extension zend_extension = "C:\xampp\php\ext\php_xdebug.dll" which seems to be working, having tested some broken code and got the nice standard orange error notice. However, having read this question, http://stackoverflow.com/questions/133686/what-is-the-best-way-to-profile-php-code and enabled the profiler, I cannot seem to create a cachegrind file. Many of the guides that I've looked at seem to think you need to install XDebug in XAMPP which leads me to think they are out of date, as XDebug is bundled with XAMPP these days. So I would appreciate it if anyone can help point me in the right direction with both configuring XDebug to output grind files, and or just a great set of default settings for the XDebug config in XAMPP. Seems there is very little documentation to go on. If people have tips on integrating these tools with Netbeans, that would be awesomesauce. I'm happy to get suggestions on other things that I can do to help tighten up my php code, both syntactically and performance wise Thanks, and apologies for the rambling question(s)! Ninja edit I should menion that I'm using named vhosts as my Apache configuration, which I think is why running XDebug on port 9000 isn't working for me. I guess I'd need to edit my vhost to include port 9000

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• How to motivate as a project leader?

  - by Zenzen

  Ok so some of you might think this is not stackoverflow related, but since I got a similar question during an interview (for a J2EE dev position) I think you guys will help me in the end. The situation is simple: you're working on a project in a small group (4-5 people), you're the project leader and the guy who's the most competent (technology wise) is also slacking the most. What do you do to motivate him? The problem is, I'm having the same issue at the university - this semester we have a lot of projects going on (6 to be exact) so we decided to dived the work so everyone will do 1-2 projects in a technology he knows/wants to learn. It's been working well for the most part, the problem is the person whom we thought would finish his project way before us as he's the most experienced among us. How am I supposed to make him do his share properly? Till now he was just half assing his part by doing the bare minimum, with which the professor wasn't really pleased to say the least... Now it's only a university project, but in the future I might have the same problem in a real job and losing a really smart and experienced worker (as firing him is the only solution I can come up with now) would really be a waste. Aren't there any better ways? p.s. now that I think about it, are there any books that would help me in becoming a better project manager?

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• What is the preferred way in C++ for converting a builtin type (int) to bool?

  - by Martin

  When programming with Visual C++, I think every developer is used to see the warning warning C4800: 'BOOL' : forcing value to bool 'true' or 'false' from time to time. The reason obviously is that BOOL is defined as int and directly assigning any of the built-in numerical types to bool is considered a bad idea. So my question is now, given any built-in numerical type (int, short, ...) that is to be interpreted as a boolean value, what is the/your preferred way of actually storing that value into a variable of type bool? Note: While mixing BOOL and bool is probably a bad idea, I think the problem will inevitably pop up whether on Windows or somewhere else, so I think this question is neither Visual-C++ nor Windows specific. Given int nBoolean; I prefer this style: bool b = nBoolean?true:false; The following might be alternatives: bool b = !!nBoolean; bool b = (nBoolean != 0); Is there a generally preferred way? Rationale? I should add: Since I only work with Visual-C++ I cannot really say if this is a VC++ specific question or if the same problem pops up with other compilers. So it would be interesting to specifically hear from g++ or users how they handle the int-bool case. Regarding Standard C++: As David Thornley notes in a comment, the C++ Standard does not require this behavior. In fact it seems to explicitly allow this, so one might consider this a VC++ weirdness. To quote the N3029 draft (which is what I have around atm.): 4.12 Boolean conversions [conv.bool] A prvalue of arithmetic, unscoped enumeration, pointer, or pointer to member type can be converted to a prvalue of type bool. A zero value, null pointer value, or null member pointer value is converted to false; any other value is converted to true. (...)

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• In Inform 7, is it possible to use a second noun construct with "pull"?

  - by Beska

  I'll eat my hat if I get a good answer to this...I suspect that although I'm a rank beginner in Inform 7, and I'm guessing this isn't that hard, but there are probably not many people here who are familiar with Inform 7. Still, nothing ventured... I'm trying to create a custom response to a "pull" action. Unfortunately, I think the "pull" action doesn't normally expect a second noun. So I'm trying something like this: The nails are some things in the Foyer. The nails are scenery. Instead of pulling the nails: If the second noun is nothing: say "How? Are you going to pull the nails with your teeth?"; otherwise: say "I don't think that's going to do the job." But while this compiles, and the first part works, the "I don't think..." section is never called...the interpreter just responds "I only understood you as far as wanting to pull the nails." Do I have to create my own custom action for this? Overwrite the standard pull action? Am I missing something simple that will allow me to get this to work?

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• Simplest PHP Routing framework .. ?

  - by David

  I'm looking for the simplest implementation of a routing framework in PHP, in a typical PHP environment (Running on Apache, or maybe nginx) .. It's the implementation itself I'm mostly interested in, and how you'd accomplish it. I'm thinking it should handle URL's, with the minimal rewriting possible, (is it really a good idea, to have the same entrypoint for all dynamic requests?!), and it should not mess with the querystring, so I should still be able to fetch GET params with $_GET['var'] as you'd usually do.. So far I have only come across .htaccess solutions that puts everything through an index.php, which is sort of okay. Not sure if there are other ways of doing it. How would you "attach" what URL's fit to what controllers, and the relation between them? I've seen different styles. One huge array, with regular expressions and other stuff to contain the mapping. The one I think I like the best is where each controller declares what map it has, and thereby, you won't have one huge "global" map, but a lot of small ones, each neatly separated. So you'd have something like: class Root { public $map = array( 'startpage' => 'ControllerStartPage' ); } class ControllerStartPage { public $map = array( 'welcome' => 'WelcomeControllerPage' ); } // Etc ... Where: 'http://myapp/' // maps to the Root class 'http://myapp/startpage' // maps to the ControllerStartPage class 'http://myapp/startpage/welcome' // maps to the WelcomeControllerPage class 'http://myapp/startpage/?hello=world' // Should of course have $_GET['hello'] == 'world' What do you think? Do you use anything yourself, or have any ideas? I'm not interested in huge frameworks already solving this problem, but the smallest possible implementation you could think of. I'm having a hard time coming up with a solution satisfying enough, for my own taste. There must be something pleasing out there that handles a sane bootstrapping process of a PHP application without trying to pull a big magic hat over your head, and force you to use "their way", or the highway! ;)

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• Manually filling opcode cache for entire app using apc_compile_file, then switching to new release.

  - by Ben

  Does anyone have a great system, or any ideas, for doing as the title says? I want to switch production version of web app-- written in PHP and served by Apache-- from release 1234 to release 1235, but before that happens, have all files already in the opcode cache (APC). Then after the switch, remove the old cache entries for files from release 1234. As far as I can think of there are three easy ways of atomically switching from one version to the next. Have a symbolic link, for example /live, that is always the document root but is changed to point from one version to the next. Similarly, have a directory /live that is always the document root, but use mv live oldversion && mv newversion live to switch to new version. Edit apache configuration to change the document root to newversion, then restart apache. I think it is preferable not to have to do 3, but I can't think of anyway to precompile all php files AND use 1 or 2 to switch release. So can someone either convince me its okay to rely on option 3, or tell me how to work with 1 or 2, or reveal some other option I am not thinking of?

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• why do we need advanced knowledge of mathematics & physics for programming?

  - by Sumeet

  Guys, I have been very good in mathematics and physics in my schools and colleges. Right now I am a programmer. Even in the colleges I have to engrossed my self into computers and programming things all the time. As I used to like it very much. But I have always felt the lack of advanced mathematics and physics in all the work I have done (Programs). Programming never asked me any advanced mathematics and physics knowledge in what I was very good. It always ask u some optimized loops, and different programming technologies which has never been covered in advanced mathematics and physics. Even at the time of selection in big College , such a kind of advanced knowledge is required. Time by time I got out of touch of all that facts and concepts (advanced mathematics and physics). And now after, 5 years in job I found it hard to resolve Differentiations and integrations from Trigonometry. Which sometimes make me feel like I have wasted time in those concepts because they are never used. (At that time I knew that I am going to be a programmer) If one need to be a programmer why do all this advanced knowledge is required. One can go with elementry knowledge a bit more. You never got to think like scientists and R&D person in your Schols and colleges for being a programmer? Just think and let me know your thoughts. I must be wrong somewhere in what I think , but not able to figure that out..? Regards Sumeet

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• about c# OBJECTS and the Possibilties it has.

  - by user527825

  As a novice programmer and i always wonder about c# capabilities.i know it is still early to judge that but all i want to know is can c# do complex stuffs or something outside windows OS. 1- I think c# is a proprietary language (i don't know if i said that right) meaning you can't do it outside visual studio or windows. 2-also you cant create your own controller(called object right?) like you are forced to use these available in toolbox and their properties and methods. 3-can c# be used with openGL API or DirectX API . 4-Finally it always bothers me when i think i start doing things in visual studio, i know it sounds arrogant to say but sometimes i feel that i don't like to be forced to use something even if its helpful, like i feel (do i have the right to feel?) that i want to do all things by myself? don't laugh i just feel that this will give me a better understanding. 5- is visual c# is like using MaxScript inside 3ds max in that c# is exclusive to do windows and forms and components that are windows related and maxscript is only for 3d editing and manipulation for various things in the software. If it is too difficult for a beginner i hope you don't answer the fourth question as i don't have enough motivation and i want to keep the little i have. thank you for your time. Note: 1-sorry for my English, i am self taught and never used the language with native speakers so expect so errors. 2-i have a lot of questions regarding many things, what is the daily ratio you think for asking (number of questions) that would not bother the admins of the site and the members here. thank you for your time.

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• Time complexity to fill hash table (homework)?

  - by Heathcliff

  This is a homework question, but I think there's something missing from it. It asks: Provide a sequence of m keys to fill a hash table implemented with linear probing, such that the time to fill it is minimum. And then Provide another sequence of m keys, but such that the time fill it is maximum. Repeat these two questions if the hash table implements quadratic probing I can only assume that the hash table has size m, both because it's the only number given and because we have been using that letter to address a hash table size before when describing the load factor. But I can't think of any sequence to do the first without knowing the hash function that hashes the sequence into the table. If it is a bad hash function, such that, for instance, it hashes every entry to the same index, then both the minimum and maximum time to fill it will take O(n) time, regardless of what the sequence looks like. And in the average case, where I assume the hash function is OK, how am I suppossed to know how long it will take for that hash function to fill the table? Aren't these questions linked to the hash function stronger than they are to the sequence that is hashed? As for the second question, I can assume that, regardless of the hash function, a sequence of size m with the same key repeated m-times will provide the maximum time, because it will cause linear probing from the second entry on. I think that will take O(n) time. Is that correct? Thanks

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• Block facebook from my website

  - by Joseph Szymborski

  I have a secure link direction service I'm running (expiringlinks.co). If I change the headers in php to redirect my visitors, then facebook is able to show a preview of the website I'm redirecting to when users send links to one another via facebook. I wish to avoid this. Right now, I'm using an AJAX call to get the URL and javascript to redirect, but it's causing problems for users who don't use javascript. Here are a number of ways I'd like to block facebook, but I can't seem to get working: I've tried blocking the facebook bot (facebookexternalhit/1.0 and facebookexternalhit/1.1) but it's not working, I don't think they're using them for this functionality. I'm thinking of blocking the facebook IP addresses, but I can't find all of them, and I don't think it'll work unless I get all of them. I've thought of using a CAPTCHA or even a button, but I can't bring myself to do that to my visitors. Not to mention I don't think anyone would use the site. I've searched the facebook docs for meta tags that would "opt-me out", but haven't found one, and doubt that I would trust it if I had. Any creative ideas or any idea how to implement the ones above? Thank you so much in advance!

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• Projects integration question

  - by qkrsppopcmpt

  Other team has one legacy system, which is data aggregators. It is implemented as web service using JAVA, SOAP,MTOM,Tomcat and Axis2. They have wsdl files defining functionalities such as search, retrieve data, upload, download. Our team has a new developed website which is developed using RoR with mySQL. It is sort of social networking. Users can register, add friends, upload images, videos. Also, they can search data. We are required to connect the two systems. One possible solution I think is - Adding components into our website. The component invoke services on the aggregators. - Synchronize website database to the aggregators. My doubts are: 1. How to add components in our websites? The components should use Java or Ruby or adapter from java to ruby. It is possible using ruby invoke web service. I think it should work since it is the point of web service. If so, can ruby call those services in wsdl directly? But how to deal with those different data structure? How to synchroinze our database to the aggregators. I think the best way is also through web service invocation such as upload. That means, we have to export the db records into xml files and then write some tools to upload. The web service project support MTOM. So, it is fine to upload huge data. Am I on the right record? Can anybody give me some hint. Thanks.

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• Haskell Cons Operator (:)

  - by Carson Myers

  I am really new to Haskell (Actually I saw "Real World Haskell" from O'Reilly and thought "hmm, I think I'll learn functional programming" yesterday) and I am wondering: I can use the construct operator to add an item to the beginning of a list: 1 : [2,3] [1,2,3] I tried making an example data type I found in the book and then playing with it: --in a file data BillingInfo = CreditCard Int String String | CashOnDelivery | Invoice Int deriving (Show) --in ghci $ let order_list = [Invoice 2345] $ order_list [Invoice 2345] $ let order_list = CashOnDelivery : order_list $ order_list [CashOnDelivery, CashOnDelivery, CashOnDelivery, CashOnDelivery, CashOnDelivery, CashOnDelivery, CashOnDelivery, CashOnDelivery, CashOnDelivery, CashOnDelivery, CashOnDelivery, CashOnDelivery, CashOnDelivery, CashOnDelivery, ...- etc... it just repeats forever, is this because it uses lazy evaluation? -- EDIT -- okay, so it is being pounded into my head that let order_list = CashOnDelivery:order_list doesn't add CashOnDelivery to the original order_list and then set the result to order_list, but instead is recursive and creates an infinite list, forever adding CashOnDelivery to the beginning of itself. Of course now I remember that Haskell is a functional language and I can't change the value of the original order_list, so what should I do for a simple "tack this on to the end (or beginning, whatever) of this list?" Make a function which takes a list and BillingInfo as arguments, and then return a list? -- EDIT 2 -- well, based on all the answers I'm getting and the lack of being able to pass an object by reference and mutate variables (such as I'm used to)... I think that I have just asked this question prematurely and that I really need to delve further into the functional paradigm before I can expect to really understand the answers to my questions... I guess what i was looking for was how to write a function or something, taking a list and an item, and returning a list under the same name so the function could be called more than once, without changing the name every time (as if it was actually a program which would add actual orders to an order list, and the user wouldn't have to think of a new name for the list each time, but rather append an item to the same list).

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• Fastest inline-assembly spinlock

  - by sigvardsen

  I'm writing a multithreaded application in c++, where performance is critical. I need to use a lot of locking while copying small structures between threads, for this I have chosen to use spinlocks. I have done some research and speed testing on this and I found that most implementations are roughly equally fast: Microsofts CRITICAL_SECTION, with SpinCount set to 1000, scores about 140 time units Implementing this algorithm with Microsofts InterlockedCompareExchange scores about 95 time units Ive also tried to use some inline assembly with __asm {} using something like this code and it scores about 70 time units, but I am not sure that a proper memory barrier has been created. Edit: The times given here are the time it takes for 2 threads to lock and unlock the spinlock 1,000,000 times. I know this isn't a lot of difference but as a spinlock is a heavily used object, one would think that programmers would have agreed on the fastest possible way to make a spinlock. Googling it leads to many different approaches however. I would think this aforementioned method would be the fastest if implemented using inline assembly and using the instruction CMPXCHG8B instead of comparing 32bit registers. Furthermore memory barriers must be taken into account, this could be done by LOCK CMPXHG8B (I think?), which guarantees "exclusive rights" to the shared memory between cores. At last [some suggests] that for busy waits should be accompanied by NOP:REP that would enable Hyper-threading processors to switch to another thread, but I am not sure whether this is true or not? From my performance-test of different spinlocks, it is seen that there is not much difference, but for purely academic purpose I would like to know which one is fastest. However as I have extremely limited experience in the assembly-language and with memory barriers, I would be happy if someone could write the assembly code for the last example I provided with LOCK CMPXCHG8B and proper memory barriers in the following template: __asm { spin_lock: ;locking code. spin_unlock: ;unlocking code. }

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• What makes an effective UI for displaying versioning of structured hierarchical data

  - by Fadrian Sudaman

  Traditional version control system are displaying versioning information by grouping Projects-Folders-Files with Tree view on the left and details view on the right, then you will click on each item to look at revision history for that configuration history. Assuming that I have all the historical versioning information available for a project from Object-oriented model perspective (e.g. classes - methods - parameters and etc), what do you think will be the most effective way to present such information in UI so that you can easily navigate and access the snapshot view of the project and also the historical versioning information? Put yourself in the position that you are using a tool like this everyday in your job like you are currently using SVN, SS, Perforce or any VCS system, what will contribute to the usability, productivity and effectiveness of the tool. I personally find the classical way for display folders and files like above are very restrictive and less effective for displaying deep nested logical models. Assuming that this is a greenfield project and not restricted by specific technology, how do you think I should best approach this? I am looking for idea and input here to add values to my research project. Feel free to make any suggestions that you think is valuable. Thanks again for anyone that shares their thoughts.

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• Wrapping unmanaged C++ with C++/CLI - a proper approach.

  - by Jamie

  Hi there, as stated in the title, I want to have my old C++ library working in managed .NET. I think of two possibilities: 1) I might try to compile the library with /clr and try "It Just Works" approach. 2) I might write a managed wrapper to the unmanaged library. First of all, I want to have my library working FAST, as it was in unmanaged environment. Thus, I am not sure if the first approach will not cause a large decrease in performance. However, it seems to be faster to implement (not a right word :-)) (assuming it will work for me). On the other hand, I think of some problems that might appear while writing a wrapper (e.g. how to wrap some STL collection (vector for instance)?) I think of writing a wrapper residing in the same project as the unmanaged C++ resides - is that a reasonable approach (e.g. MyUnmanagedClass and MyManagedClass in the same project, the second wrapping the other)? What would you suggest in that problem? Which solution is going to give me better performance of the resulting code? Thank you in advance for any suggestions and clues! Cheers

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• Accurately and securely measure the time spent viewing a web page

  - by balpha

  Suppose the following: You have a web page that presents a simple game to a user (e.g. a quiz, a puzzle, etc). The user solves the puzzle, submits the result, and you want to measure as precisely as possible how long they took to solve it. Assume it's quite simple, so we're talking seconds, not hours. Also assume JavaScript is required anyway, so there's no need to think of JS-disabled browsers. Finally, assume we don't want to use anything like Flash, Silverlight, or the like. I can think of several techniques: Simply take the time between the points when the data was sent from the server and when the submission arrives. Since this is exclusively server-side, there's no chance for cheating. However, issues like network latency and page rendering time might make this unfair for users with slow computers / browsers / internet connections. On the first request, just send the page without the actual game data. When everything is loaded so far, retrieve the game data through an AJAX call and populate it into the page. This is similar to 1., but reduces some of the caveats introduced through time spent on overhead. Have the time measured on the client side using JavaScript and submitted alongside with the solution. This would theoretically be the most accurate, but it introduces the possibility of cheating, because you're relying on client data. Use the request time headers of a "ready to play" AJAX call and the result submission request. Same caveat as 3., as it is still client data. A combination of server side and client side measuring with some kind of plausibility analysis. I can't think of a good way, but maybe you can. Thoughts? Other ideas?

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