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• My program is spending most of its time in objc_msgSend. Does that mean that Objective-C has bad per

  - by Paperflyer

  Hello Stackoverflow. I have written an application that has a number of custom views and generally draws a lot of lines and bitmaps. Since performance is somewhat critical for the application, I spent a good amount of time optimizing draw performance. Now, activity monitor tells me that my application is usually using about 12% CPU and Instrument (the profiler) says that a whopping 10% CPU is spent in objc_msgSend (mostly in drawing related system calls). On the one hand, I am glad about this since it means that my drawing is about as fast as it gets and my optimizations where a huge success. On the other hand, it seems to imply that the only thing that is still using my CPU is the Objective-C overhead for messages (objc_msgSend). Hence, that if I had written the application in, say, Carbon, its performance would be drastically better. Now I am tempted to conclude that Objective-C is a language with bad performance, even though Cocoa seems to be awfully efficient since it can apparently draw faster than Objective-C can send messages. So, is Objective-C really a language with bad performance? What do you think about that?

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• How to copy a variable in JavaScript?

  - by Michael Stum

  I have this JavaScript code: for (var idx in data) { var row = $("<tr></tr>"); row.click(function() { alert(idx); }); table.append(row); } So I'm looking through an array, dynamically creating rows (the part where I create the cells is omitted as it's not important). Important is that I create a new function which encloses the idx variable. However, idx is only a reference, so at the end of the loop, all rows have the same function and all alert the same value. One way I solve this at the moment is by doing this: function GetRowClickFunction(idx){ return function() { alert(idx); } } and in the calling code I call row.click(GetRowClickFunction(idx)); This works, but is somewhat ugly. I wonder if there is a better way to just copy the current value of idx inside the loop? While the problem itself is not jQuery specific (it's related to JavaScript closures/scope), I use jQuery and hence a jQuery-only solution is okay if it works.

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• Any guidelines for handling the Headset and Bluetooth AVRC transport controls in Android 2.2

  - by StefanK

  I am trying to figure out what is the correct (new) approach for handling the Intent.ACTION_MEDIA_BUTTON in Froyo. In pre 2.2 days we had to register a BroadcastReceiver (either permanently or at run-time) and the Media Button events would arrive, as long as no other application intercepts them and aborts the broadcast. Froyo seems to still somewhat support that model (at least for the wired headset), but it also introduces the registerMediaButtonEventReceiver, and unregisterMediaButtonEventReceiver methods that seem to control the "transport focus" between applications. During my experiments, using registerMediaButtonEventReceiver does cause both the bluetooth and the wired headset button presses to be routed to the application's broadcast receiver (the app gets the "transport focus"), but it looks like any change in the audio routing (for example unplugging the headset) shits the focus back to the default media player. What is the logic behind the implementation in Android 2.2? What is correct way to handle transport controls? Do we have to detect the change in the audio routing and try to re-gain the focus? This is an issue that any 3rd party media player on the Android platform has to deal with, so I hope that somebody (probably a Google Engineer) can provide some guidelines that we can all follow. Having a standard approach may make headset button controls a bit more predictable for the end users. Stefan

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• Enterprise Platform in Python, Design Advice

  - by Jason Miesionczek

  I am starting the design of a somewhat large enterprise platform in Python, and was wondering if you guys can give me some advice as to how to organize the various components and which packages would help achieve the goals of scalability, maintainability, and reliability. The system is basically a service that collects data from various outside sources, with each outside source having its own separate application. These applications would poll a central database and get any requests that have been submitted to perform on the external source. There will be a main website and REST/SOAP API that should also have access to the central data service. My initial thought was to use Django for the web site, web service and data access layer (using its built-in ORM), and then the outside source applications can use the web service(s) to get the information they need to process the request and save the results. Using this method would allow me to have multiple instances of the service applications running on the same or different machines to balance out the load. Are there more elegant means of accomplishing this? i've heard of messaging systems such as MQ, would something like that be beneficial in this scenario? My other thought was to use a completely separate data service not based on Django, and use some kind of remoting or remote objects (in they exist in Python) to interact with the data model. The downside here would be with the website which would become much slower if it had to push all of its data requests through a second layer. I would love to hear what other developers have come up with to achieve these goals in the most flexible way possible.

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• How to mix Grammer (Rules) & Dictation (Free speech) with SpeechRecognizer in C#

  - by Lee Englestone

  I really like Microsofts latest speech recognition (and SpeechSynthesis) offerings. http://msdn.microsoft.com/en-us/library/ms554855.aspx http://estellasays.blogspot.com/2009/04/speech-recognition-in-cnet.html However I feel like I'm somewhat limited when using grammers. Don't get me wrong grammers are great for telling the speech recognition exactly what words / phrases to look out for, however what if I want it to recognise something i've not given it a heads up about? Or I want to parse a phrase which is half pre-determined command name and half random words? For example.. Scenario A - I say "Google [Oil Spill]" and I want it to open Google with search results for the term in brackets which could be anything. Scenario B - I say "Locate [Manchester]" and I want it to search for Manchester in Google Maps or anything else non pre-determined I want it to know that 'Google' and 'Locate' are commands and what comes after it are parameters (and could be anything). Question : Does anyone know how to mix the use of pre-determined grammers (words the speech recognition should recognise) and words not in its pre-determined grammer? Code fragments.. using System.Speech.Recognition; ... ... SpeechRecognizer rec = new SpeechRecognizer(); rec.SpeechRecognized += rec_SpeechRecognized; var c = new Choices(); c.Add("search"); var gb = new GrammarBuilder(c); var g = new Grammar(gb); rec.LoadGrammar(g); rec.Enabled = true; ... ... void rec_SpeechRecognized(object sender, SpeechRecognizedEventArgs e) { if (e.Result.Text == "search") { string query = "How can I get a word not defined in Grammer recognised and passed into here!"; launchGoogle(query); } } ... ... private void launchGoogle(string term) { Process.Start("IEXPLORE", "google.com?q=" + term); }

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• Alter a function as a parameter before evaluating it in R?

  - by Shane

  Is there any way, given a function passed as a parameter, to alter its input parameter string before evaluating it? Here's pseudo-code for what I'm hoping to achieve: test.func <- function(a, b) { # here I want to alter the b expression before evaluating it: b(..., val1=a) } Given the function call passed to b, I want to add in a as another parameter without needing to always specify ... in the b call. So the output from this test.func call should be: test.func(a="a", b=paste(1, 2)) "1" "2" "a" Edit: Another way I could see doing something like this would be if I could assign the additional parameter within the scope of the parent function (again, as pseudo-code); in this case a would be within the scope of t1 and hence t2, but not globally assigned: t2 <- function(...) { paste(a=a, ...) } t1 <- function(a, b) { local( { a <<- a; b } ) } t1(a="a", b=t2(1, 2)) This is somewhat akin to currying in that I'm nesting the parameter within the function itself. Edit 2: Just to add one more comment to this: I realize that one related approach could be to use "prototype-based programming" such that things would be inherited (which could be achieved with the proto package). But I was hoping for a easier way to simply alter the input parameters before evaluating in R.

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• What goes into main function?

  - by Woltan

  I am looking for a best practice tip of what goes into the main function of a program using c++. Currently I think two approaches are possible. (Although the "margins" of those approaches can be arbitrarily close to each other) 1: Write a "Master"-class that receives the parameters passed to the main function and handle the complete program in that "Master"-class (Of course you also make use of other classes). Therefore the main function would be reduced to a minimum of lines. #include "MasterClass.h" int main(int args, char* argv[]) { MasterClass MC(args, argv); } 2: Write the "complete" program in the main function making use of user defined objects of course! However there are also global functions involved and the main function can get somewhat large. I am looking for some general guidelines of how to write the main function of a program in c++. I came across this issue by trying to write some unit test for the first approach, which is a little difficult since most of the methods are private. Thx in advance for any help, suggestion, link, ...

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• How to alter Postgres table data based on its contents?

  - by williamjones

  This is probably a super simple question, but I'm struggling to come up with the right keywords to find it on Google. I have a Postgres table that has among its contents a column of type text named content_type. That stores what type of entry is stored in that row. There are only about 5 different types, and I decided I want to change one of them to display as something else in my application (I had been directly displaying these). It struck me that it's funny that my view is being dictated by my database model, and I decided I would convert the types being stored in my database as strings into integers, and enumerate the possible types in my application with constants that convert them into their display names. That way, if I ever got the urge to change any category names again, I could just change it with one alteration of a constant. I also have the hunch that storing integers might be somewhat more efficient than storing text in the database. First, a quick threshold question of, is this a good idea? Any feedback or anything I missed? Second, and my main question, what's the Postgres command I could enter to make an alteration like this? I'm thinking I could start by renaming the old content_type column to old_content_type and then creating a new integer column content_type. However, what command would look at a row's old_content_type and fill in the new content_type column based off of that?

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• how do I hide certain part of form

  - by yogsma

  I have a form and it contains dropdown box and different div items. Based on selection from dropdown box, I show those div items. But some of the text in those div items are shown when the form is loaded and not when I select the option from dropdown box. The code is somewhat like this <form> <select id=""> <option value="one"> One </option> <option value="two"> Two </option> <option value="three"> Three </option> </select> <div id="onee"> header text ..<table> </table></div> <div id="twoo"> header text ..<table> </table></div> </form> So when I load the page form with select drop down box is shown , but it also shows header text which is within div. How do I hide that text?

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• Best practice- How to team-split a django project while still allowing code reusal

  - by Infinity

  I know this sounds kind of vague, but please let me explain- I'm starting work on a brand new project, it will have two main components: "ACME PRODUCT" (think Gmail, Meebo, etc), and "THE SITE" (help, information, marketing stuff, promotional landing pages, etc lots of marketing-induced cruft). So basically the url /acme/* will load stuff in the uber cool ajaxy application, and every other URI will load stuff in the other site. Problem: "THE SITE" component is out of my hands, and will be handled by a consultants team that will work closely with marketing, And I and my team will work solely on the ACME PRODUCT. Question: How to set up the django project in such a way that we can have: Seperate releases. (They can push new marketing pages and functionality without having to worry about the state of our code. Maybe even separate Subversion "projects") Minimize impact (on our product) of whatever flying-unicorns-hocus-pocus the other team codes into the site. Still allow some code reusal. My main concern is that the ACME product needs to be rock solid, and therefore needs to be somewhat isolated of whatever mistakes/code bloopers the consultants make in their marketing side of the site. How have you handled this? Any ideas? Thanks!

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• How to make BoxLayout vertical but children flow top-aligned?

  - by user291701

  I'm trying to get get a vertical, top-aligned layout to work. This is what I have: JPanel pane = new JPanel(); pane.setLayout(new BoxLayout(pane, BoxLayout.Y_AXIS)); MyImagePanel panelImage = new MyImagePanel(); panelImage.setSize(400, 400); pane.add(new JComboBox()); pane.add(panelImage); pane.add(new JButton("1")); pane.add(new JButton("2")); pane.add(new JButton("3")); JFrame frame = new JFrame("Title"); frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); frame.setSize(800, 600); frame.add(pane); frame.pack(); frame.setVisible(true); All the controls appear, but it looks like padding is being applied at run time between their tops and bottoms so they're somewhat vertically centered. This is what I'm going for: ----------------------------------------------------- | ComboBox | | ------------ | | | | | Image | | | | | ------------ | | Button 1 | Any additional space fills the right | ------------ | | Button 2 | | ------------ | | Button 3 | | ------------ | | | | Any additional space fills the bottom | | | ----------------------------------------------------- How do I get BoxLayout to do that? Thanks ------------------------- Update ------------------------- Was able to use this: Box vertical = Box.createVerticalBox(); frame.add(vertical, BorderLayout.NORTH); vertical.add(new JComboBox()); vertical.add(new JButton("1")); ... to get what I wanted.

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• Best way to carry & modify a variable through various instances and functions?

  - by bobsoap

  I'm looking for the "best practice" way to achieve a message / notification system. I'm using an OOP-based approach for the script and would like to do something along the lines of this: if(!$something) $messages->add('Something doesn\'t exist!'); The add() method in the messages class looks somewhat like this: class messages { public function add($new) { $messages = $THIS_IS_WHAT_IM_LOOKING_FOR; //array $messages[] = $new; $THIS_IS_WHAT_IM_LOOKING_FOR = $messages; } } In the end, there is a method in which reads out $messages and returns every message as nicely formatted HTML. So the questions is - what type of variable should I be using for $THIS_IS_WHAT_IM_LOOKING_FOR? I don't want to make this use the database. Querying the db every time just for some messages that occur at runtime and disappear after 5 seconds just seems like overkill. Using global constants for this is apparently worst practice, since constants are not meant to be variables that change over time. I don't even know if it would work. I don't want to always pass in and return the existing $messages array through the method every time I want to add a new message. I even tried using a session var for this, but that is obviously not suited for this purpose at all (it will always be 1 pageload too late). Any suggestions? Thanks!

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• How best to implement support for multiple devices in a web application.

  - by Kabeer

  Hello. My client would like a business application to support 'every possible device'. The application in question is essentially a web application and 'every possible device', I believe encompasses mobile phones, netbooks, ipad, other browser supporting devices, etc. The application is somewhat complex w.r.t. the data it captures and other functions it performs (reporting). If I continue to honor increasing complexity in the application, I guess there are more chances of it not working on other devices. I'd like to know how web applications support multiple devices conventionally? Are there multiple versions of presentation layer (like many times I find m.website.com dedicated for mobile devices)? Further, if my application is to take advantage of Java Script, RIA (Flash, SilverLight) then what are the consequences and workarounds? Mine is a .Net based application and the stack also contains Ext JS Java Script library. While I would like to use it for sure, considering that I would be doing a lot of work in Java Script rather than HTML, this could be a problem. The answer to the above could be descriptive. If there is something already prescribed out there, please share the link(s). Thanks.

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• User Defined Conversions in C++

  - by wash

  Recently, I was browsing through my copy of the C++ Pocket Reference from O'Reilly Media, and I was surprised when I came across a brief section and example regarding user-defined conversion for user-defined types: #include <iostream> class account { private: double balance; public: account (double b) { balance = b; } operator double (void) { return balance; } }; int main (void) { account acc(100.0); double balance = acc; std::cout << balance << std::endl; return 0; } I've been programming in C++ for awhile, and this is the first time I've ever seen this sort of operator overloading. The book's description of this subject is somewhat brief, leaving me with a few unanswered questions about this feature: Is this a particularly obscure feature? As I said, I've been programming in C++ for awhile and this is the first time I've ever come across this. I haven't had much luck finding more in-depth material regarding this. Is this relatively portable? (I'm compiling on GCC 4.1) Can user-defined conversions to user defined types be done? e.g. operator std::string () { /* code */ }

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• Why is T() = T() allowed?

  - by Rimo

  I believe the expression T() creates an rvalue (by the Standard). However, the following code compiles (at least on gcc4.0): class T {}; int main() { T() = T(); } I know technically this is possible because member functions can be invoked on temporaries and the above is just invoking the operator= on the rvalue temporary created from the first T(). But conceptually this is like assigning a new value to an rvalue. Is there a good reason why this is allowed? Edit: The reason I find this odd is it's strictly forbidden on built-in types yet allowed on user-defined types. For example, int(2) = int(3) won't compile because that is an "invalid lvalue in assignment". So I guess the real question is, was this somewhat inconsistent behavior built into the language for a reason? Or is it there for some historical reason? (E.g it would be conceptually more sound to allow only const member functions to be invoked on rvalue expressions, but that cannot be done because that might break some existing code.)

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• power and modulo on the fly for big numbers

  - by user unknown

  I raise some basis b to the power p and take the modulo m of that. Let's assume b=55170 or 55172 and m=3043839241 (which happens to be the square of 55171). The linux-calculator bc gives the results (we need this for control): echo "p=5606;b=55171;m=b*b;((b-1)^p)%m;((b+1)^p)%m" | bc 2734550616 309288627 Now calculating 55170^5606 gives a somewhat large number, but since I have to do a modulooperation, I can circumvent the usage of BigInt, I thought, because of: (a*b) % c == ((a%c) * (b%c))%c i.e. (9*7) % 5 == ((9%5) * (7%5))%5 => 63 % 5 == (4 * 2) %5 => 3 == 8 % 5 ... and a^d = a^(b+c) = a^b * a^c, therefore I can divide b+c by 2, which gives, for even or odd ds d/2 and d-(d/2), so for 8^5 I can calculate 8^2 * 8^3. So my (defective) method, which always cut's off the divisor on the fly looks like that: def powMod (b: Long, pot: Int, mod: Long) : Long = { if (pot == 1) b % mod else { val pot2 = pot/2 val pm1 = powMod (b, pot, mod) val pm2 = powMod (b, pot-pot2, mod) (pm1 * pm2) % mod } } and feeded with some values, powMod (55170, 5606, 3043839241L) res2: Long = 1885539617 powMod (55172, 5606, 3043839241L) res4: Long = 309288627 As we can see, the second result is exactly the same as the one above, but the first one looks quiet different. I'm doing a lot of such calculations, and they seem to be accurate as long as they stay in the range of Int, but I can't see any error. Using a BigInt works as well, but is way too slow: def calc2 (n: Int, pri: Long) = { val p: BigInt = pri val p3 = p * p val p1 = (p-1).pow (n) % (p3) val p2 = (p+1).pow (n) % (p3) print ("p1: " + p1 + " p2: " + p2) } calc2 (5606, 55171) p1: 2734550616 p2: 309288627 (same result as with bc) Can somebody see the error in powMod?

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• Best way to build an application based on R?

  - by Prasad Chalasani

  I'm looking for suggestions on how to go about building an application that uses R for analytics, table generation, and plotting. What I have in mind is an application that: displays various data tables in different tabs, somewhat like in Excel, and the columns should be sortable by clicking. takes user input parameters in some dialog windows. displays plots dynamically (i.e. user-input-dependent) either in a tab or in a new pop-up window/frame Note that I am not talking about a general-purpose fron-end/GUI for exploring data with R (like say Rattle), but a specific application. Some questions I'd like to see addressed are: Is an entirely R-based approach even possible ( on Windows ) ? The following passage from the Rattle article in R-Journal intrigues me: It is interesting to note that the first implementation of Rattle actually used Python for implementing the callbacks and R for the statistics, using rpy. The release of RGtk2 allowed the interface el- ements of Rattle to be written directly in R so that Rattle is a fully R-based application If it's better to use another language for the GUI part, which language is best suited for this? I'm looking for a language where it's relatively "painless" to build the GUI, and that also integrates very well with R. From this StackOverflow question How should I do rapid GUI development for R and Octave methods (possibly with Python)? I see that Python + PyQt4 + QtDesigner + RPy2 seems to be the best combo. Is that the consensus ? Anyone have pointers to specific (open source) applications of the type I describe, as examples that I can learn from?

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• Where can I find a powerful, standards compliant, web-based interactive org chart API?

  - by Adam Soltys

  Hi, I'm looking to build an interactive web-based org chart for a large organization. I somewhat like the interface at ancestry.com where you can hover over people and pan/zoom around and click on different nodes to make them the root. Ideally, I'd like it if people could belong to multiple organizational entities like committees, working groups, etc. In other words the API should support graphs in general, not just trees. I'd like to be able to visually explode each organizational substructure into substituents by clicking on it, with a nice animation of the employees ballooning or spilling out so you can really interactively drill down through the organization. I found http://code.google.com/apis/visualization/documentation/gallery/orgchart.html but it looks a bit rudimentary. I know there are desktop tools like OrgPlus and Visio that can build static charts but I'm really looking for a free, web-based API with open standards-based output like SVG or HTML5 Canvas elements rather than Flash or some proprietary output. Something I can embed into a custom web application and style myself. Something interactive.

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• Best (functional?) programming language to learn coming from Mathematica

  - by Will Robertson

  As a mechanical engineering PhD student, I haven't had a great pedigree in programming as part of my “day job”. I started out in Matlab (having written some Hypercard and Applescript back in the day, and being introduced to Ada, of all things, in my 1st undergrad year), learned to program—if you can call it that—in (La)TeX; and finally discovered and fell for Mathematica. Now I'm interested in learning a "real" programming language that I can enjoy in the same sort of style as Mathematica, which tries to stress functional programming since it seems to map more nicely to how certain kinds of mathematics can be written algorithmically. So which functional language should I learn? I guess the obvious answer is “as many as possible”, but let's start out humble and give a single, well-considered option a good crack. I've heard good things about, say, Haskell and Scala, but I wonder if (given my non–computer science background) I'd be better off starting in more “grounded” territory and going with Ruby or Python (the latter having the big advantage of being used for Sage, which I'd also like to investigate…after my PhD). Well, I guess this is pretty subjective, so perhaps I could rephrase: would it be better to start looking at Haskell (say) straight after an ad-hoc education to functional programming in Mathematica, or will I get more out of learning Python (say) first? In reference to the question "what do I want to do with it?", I guess my answer is "fun, and learning more". I've got this list of languages that I'd like to look at, and I don't know how to trim them down. And I'd rather start with something a little higher-level than C simply so that I can be somewhat productive without having to re-invent many wheels for any code I'd like to write.

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• Reduce file size for charts pasted from excel into word

  - by Steve Clanton

  I have been creating reports by copying some charts and data from an excel document into a word document. I am pasting into a content control, so i use ChartObject.CopyPicture in excel and ContentControl.Range.Paste in word. This is done in a loop: Set ws = ThisWorkbook.Worksheets("Charts") With ws For Each cc In wordDocument.ContentControls If cc.Range.InlineShapes.Count > 0 Then scaleHeight = cc.Range.InlineShapes(1).scaleHeight scaleWidth = cc.Range.InlineShapes(1).scaleWidth cc.Range.InlineShapes(1).Delete .ChartObjects(cc.Tag).CopyPicture Appearance:=xlScreen, Format:=xlPicture cc.Range.Paste cc.Range.InlineShapes(1).scaleHeight = scaleHeight cc.Range.InlineShapes(1).scaleWidth = scaleWidth ElseIf ... Next cc End With Creating these reports using Office 2007 yielded files that were around 6MB, but creating them (using the same worksheet and document) in Office 2010 yields a file that is around 10 times as large. After unzipping the docx, I found that the extra size comes from emf files that correspond to charts that are pasted in using VBA. Where they range from 360 to 900 KB before, they are 5-18 MB. And the graphics are not visibly better. I am able to CopyPicture with the format xlBitmap, and while that is somewhat smaller, it is larger than the emf generated by Office 2007 and noticeably poorer quality. Are there any other options for reducing the file size? Ideally, I would like to produce a file with the same resolution for the charts as I did using Office 2007. Is there any way that uses VBA only (without modifying the charts in the spreadsheet)?

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• Chicken and egg problem (restore database) when trying to write unit test against SQl Server 2008.

  - by Hamish Grubijan

  Ok, they are not unit tests but end-to-end tests. The setup is somewhat involved. Unit tests will use C#, ODBC connection. Every unit tests will try to clean up after itself, but every 20 tests or so (once per C# class) we would need to do a full database restore. I do not think I can do it over an ODBC connection, according to this document: http://www.sql-server-performance.com/articles/dba/Obtain_Exclusive_Access_to_Restore_SQL_Server_p1.aspx Msg 6104, Level 16, State 1, Line 1 Cannot use KILL to kill your own process. However, I would like to, so that 199 tests do not go amok because of a bad clean-up. Is there another way? Perhaps I can open a different "connection" such as use COM automation or something of that sort, and then kill all database connections from there? If so, how can I do that? Also, will the clients be able to re-connect automatically after a restore, or would I have to dismantle everything once every 20 tests or so? If you find this question confusing, please let me know what your questions are. Thanks!

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• Efficient and accurate way to compact and compare Python lists?

  - by daveslab

  Hi folks, I'm trying to a somewhat sophisticated diff between individual rows in two CSV files. I need to ensure that a row from one file does not appear in the other file, but I am given no guarantee of the order of the rows in either file. As a starting point, I've been trying to compare the hashes of the string representations of the rows (i.e. Python lists). For example: import csv hashes = [] for row in csv.reader(open('old.csv','rb')): hashes.append( hash(str(row)) ) for row in csv.reader(open('new.csv','rb')): if hash(str(row)) not in hashes: print 'Not found' But this is failing miserably. I am constrained by artificially imposed memory limits that I cannot change, and thusly I went with the hashes instead of storing and comparing the lists directly. Some of the files I am comparing can be hundreds of megabytes in size. Any ideas for a way to accurately compress Python lists so that they can be compared in terms of simple equality to other lists? I.e. a hashing system that actually works? Bonus points: why didn't the above method work?

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• Comparing objects and inheritance

  - by ereOn

  Hi, In my program I have the following class hierarchy: class Base // Base is an abstract class { }; class A : public Base { }; class B : public Base { }; I would like to do the following: foo(const Base& one, const Base& two) { if (one == two) { // Do something } else { // Do something else } } I have issues regarding the operator==() here. Of course comparing an instance A and an instance of B makes no sense but comparing two instances of Base should be possible. (You can't compare a Dog and a Cat however you can compare two Animals) I would like the following results: A == B = false A == A = true or false, depending on the effective value of the two instances B == B = true or false, depending on the effective value of the two instances My question is: is this a good design/idea ? Is this even possible ? What functions should I write/overload ? My apologies if the question is obviously stupid or easy, I have some serious fever right now and my thinking abilities are somewhat limited :/ Thank you.

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• Type-safe generic data structures in plain-old C?

  - by Bradford Larsen

  I have done far more C++ programming than "plain old C" programming. One thing I sorely miss when programming in plain C is type-safe generic data structures, which are provided in C++ via templates. For sake of concreteness, consider a generic singly linked list. In C++, it is a simple matter to define your own template class, and then instantiate it for the types you need. In C, I can think of a few ways of implementing a generic singly linked list: Write the linked list type(s) and supporting procedures once, using void pointers to go around the type system. Write preprocessor macros taking the necessary type names, etc, to generate a type-specific version of the data structure and supporting procedures. Use a more sophisticated, stand-alone tool to generate the code for the types you need. I don't like option 1, as it is subverts the type system, and would likely have worse performance than a specialized type-specific implementation. Using a uniform representation of the data structure for all types, and casting to/from void pointers, so far as I can see, necessitates an indirection that would be avoided by an implementation specialized for the element type. Option 2 doesn't require any extra tools, but it feels somewhat clunky, and could give bad compiler errors when used improperly. Option 3 could give better compiler error messages than option 2, as the specialized data structure code would reside in expanded form that could be opened in an editor and inspected by the programmer (as opposed to code generated by preprocessor macros). However, this option is the most heavyweight, a sort of "poor-man's templates". I have used this approach before, using a simple sed script to specialize a "templated" version of some C code. I would like to program my future "low-level" projects in C rather than C++, but have been frightened by the thought of rewriting common data structures for each specific type. What experience do people have with this issue? Are there good libraries of generic data structures and algorithms in C that do not go with Option 1 (i.e. casting to and from void pointers, which sacrifices type safety and adds a level of indirection)?

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• The Purpose of a Service Layer and ASP.NET MVC 2

  - by user332022

  In an effort to understand MVC 2 and attempt to get my company to adopt it as a viable platform for future development, I have been doing a lot of reading lately. Having worked with ASP.NET pretty exclusively for the past few years, I had some catching up to do. Currently, I understand the repository pattern, models, controllers, data annotations, etc. But there is one thing that is keeping me from completely understanding enough to start work on a reference application. The first is the Service Layer Pattern. I have read many blog posts and questions here on Stack Overflow, but I still don't completely understand the purpose of this pattern. I watched the entire video series at MVCCentral on the Golf Tracker Application and also looked at the demo code he posted and it looks to me like the service layer is just another wrapper around the repository pattern that doesn't perform any work at all. I also read this post: http://www.asp.net/Learn/mvc/tutorial-38-cs.aspx and it seemed to somewhat answer my question, however, if you are using data annotations to perform your validation, this seems unnecessary. I have looked for demonstrations, posts, etc. but I can't seem to find anything that simply explains the pattern and gives me compelling evidence to use it. Can someone please provide me with a 2nd grade (ok, maybe 5th grade) reason to use this pattern, what I would lose if I don't, and what I gain if I do?a

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