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• Benefits of migrating my work to a new web development framework?

  - by John

  When I first started programming with PHP, I was ignorant of other php frameworks (like code igniter, cake php, etc...). So I fell into the trap of re-inventing wheels, which had the benefit of being "fun" and "educational". Overtime, I discovered other open source products that I found useful, like smarty templating engine, jquery library, tcpdf library, fdf etc...so I started bundling these technologies along with things I've built over the years into a LAMP development framework to make life easier for myself. This pass year, I've been having fun developing on the code igniter framework. It does many of the things I do in my framework. Coding in CI feels natural because the MVC and ORM feels similar to the MVC and ORM of my framework. So now I'm contemplating migrating a lot of the plugins in my framework over to CI. The pros and cons I can think of for such a project are: Pros: benefit from the vast community of CI developers lots of other developers will be familiar with it better documentation Cons: I've built a lot of useful plugins against my own framework, and it will take a lot of time to move even just the essential ones at the moment, I still, work faster against my own framework than CI, just because I'm more familiar with it even if I did migrate to CI, there will always be newer and better frameworks in the near future, and i'll be contemplating this scenario again So my question is the following: perhaps I should leave my old framework as is, and for each new project I receive, I make a decision on whether the requirements are best served by developing with CI or my own framework. Is this the right approach?

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• Existing LINQ extension method similar to Parallel.For?

  - by Joel Martinez

  The linq extension methods for ienumerable are very handy ... but not that useful if all you want to do is apply some computation to each item in the enumeration without returning anything. So I was wondering if perhaps I was just missing the right method, or if it truly doesn't exist as I'd rather use a built-in version if it's available ... but I haven't found one :-) I could have sworn there was a .ForEach method somewhere, but I have yet to find it. In the meantime, I did write my own version in case it's useful for anyone else: using System.Collections; using System.Collections.Generic; public delegate void Function<T>(T item); public delegate void Function(object item); public static class EnumerableExtensions { public static void For(this IEnumerable enumerable, Function func) { foreach (object item in enumerable) { func(item); } } public static void For<T>(this IEnumerable<T> enumerable, Function<T> func) { foreach (T item in enumerable) { func(item); } } } usage is: myEnumerable.For<MyClass>(delegate(MyClass item) { item.Count++; });

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• MySQL INJECTION Solution...

  - by Val

  I have been bothered for so long by the MySQL injections and was thinking of a way to eliminate this problem all together. I have came up with something below hope that many people will find this useful. The only Draw back I can think of this is the partial search: Jo =returns "John" by using the like %% statement. Here is a php solution: <?php function safeQ(){ $search= array('delete','select');//and every keyword... $replace= array(base64_encode('delete'),base64_encode('select')); foreach($_REQUEST as $k=>$v){ str_replace($search, $replace, $v); } } foo(); function html($str){ $search= array(base64_encode('delete'),base64_encode('select')); $replace= array('delete','select');//and every keyword... str_replace($search, $replace, $str); } //example 1 ... ... $result = mysql_fetch_array($query); echo html($result[0]['field_name']); //example 2 $select = 'SELECT * FROM safeQ($_GET['query']) '; //example 3 $insert = 'INSERT INTO .... value(safeQ($_GET['query']))'; ?> I know, I know that you still could inject using 1=1 or any other type of injections... but this I think could solve half of your problem so the right mysql query is executed. So my question is if anyone can find any draw backs on this then please feel free to comment here. PLEASE GIVE AN ANSWER only if you think that this is a very useful solution and no major drawbacks are found OR you think is a bad idea all together...

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• Automatic testing of GUI related private methods

  - by Stein G. Strindhaug

  When it comes to GUI programming (at least for web) I feel that often the only thing that would be useful to unit test is some of the private methods*. While unit testing makes perfect sense for back-end code, I feel it doesn't quite fit the GUI classes. What is the best way to add automatic testing of these? * Why I think the only methods useful to test is private: Often when I write GUI classes they don't even have any public methods except for the constructor. The public methods if any is trivial, and the constructor does most of the job calling private methods. They receive some data from server does a lot of trivial output and feeds data to the constructor of other classes contained inside it, adding listeners that calls a (more or less directly) calls the server... Most of it pretty trivial (the hardest part is the layout: css, IE, etc.) but sometimes I create some private method that does some advanced tricks, which I definitely do not want to be publicly visible (because it's closely coupled to the implementation of the layout, and likely to change), but is sufficiently complicated to break. These are often only called by the constructor or repeatedly by events in the code, not by any public methods at all. I'd like to have a way to test this type of methods, without making it public or resorting to reflection trickery. (BTW: I'm currently using GWT, but I feel this applies to most languages/frameworks I've used when coding for GUI)

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• Binary Search Tree for specific intent

  - by Luís Guilherme

  We all know there are plenty of self-balancing binary search trees (BST), being the most famous the Red-Black and the AVL. It might be useful to take a look at AA-trees and scapegoat trees too. I want to do deletions insertions and searches, like any other BST. However, it will be common to delete all values in a given range, or deleting whole subtrees. So: I want to insert, search, remove values in O(log n) (balanced tree). I would like to delete a subtree, keeping the whole tree balanced, in O(log n) (worst-case or amortized) It might be useful to delete several values in a row, before balancing the tree I will most often insert 2 values at once, however this is not a rule (just a tip in case there is a tree data structure that takes this into account) Is there a variant of AVL or RB that helps me on this? Scapegoat-trees look more like this, but would also need some changes, anyone who has got experience on them can share some thougts? More precisely, which balancing procedure and/or removal procedure would help me keep this actions time-efficient?

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• A standard set of questions to ask an interviewer?

  - by Rob Wells

  We have had many questions for interviewers to ask interviewees. But none addressing information flow in the other direction, interviewee to interviewer. Just an indirect question about "deal breakers" and one about "finding dream jobs". What I'm after is when you're interviewing at a company do you have a set of questions that you like to ask to help get a feel for the company and the work environment? I have a series of questions that I like to ask that range from the development environment to testing techniques to how the team get on together. Anything else you'd like to ask? Edit: I moved my original list of interviewer questions to my answer below. I've also gone through the other answers and added the ones thought were useful in to that answer. The answer is community wiki so feel free to add anything useful. N.B. This is my first cut of categories. Feel free to modify/add/etc. the categories. Or to recategorise the questions themselves.

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• Use XML Layout to contain a simple drawing

  - by user329999

  I would like to create a simple drawing (lines, circles, squares, etc...) but I'm having difficulty figuring out the best way to do this. The drawing would need to be scaled to fit the display since the size is indirectly specified by the user (like in a CAD application). Also, I don't want to take up the entire display, leaving room for some controls (buttons, etc). I would pass the data to describe the drawing. Here's how I imagine it would work. I create an XML layout that contains something that holds the drawing (ImageView, BitmapDrawable, ShapeDrawable, ...??? not sure exactly what). Then in my Activity I would load the main XML and obtain the resource for the control that holds the drawing. I would then draw to a bitmap. Once the bitmap was completed I would load it into the control that is to hold the drawing. Somewhere along this path it would be scaled to fill the entire area allocated for the drawing in the XML layout. I don't know if my approach is the way to do this or what classes to use. I read the http://developer.android.com/guide/topics/graphics/2d-graphics.html documentation, but it's not helping me with an example. The examples I do find leave me with hints, but nothing concrete enough to do what I want, especially when it comes to scaling, using XML and/or having other controls. Also, there seems to be no good documentation on the design of the 2D drawing system in a more conceptual manner, so it makes what I read difficult to put into any useful context. Any hints on what classes would be useful and/or a good example any other reading materials? Thanks

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• AudioRecord problems with non-HTC devices

  - by Marc

  I'm having troubles using AudioRecord. An example using some of the code derived from the splmeter project: private static final int FREQUENCY = 8000; private static final int CHANNEL = AudioFormat.CHANNEL_CONFIGURATION_MONO; private static final int ENCODING = AudioFormat.ENCODING_PCM_16BIT; private int BUFFSIZE = 50; private AudioRecord recordInstance = null; ... android.os.Process.setThreadPriority(android.os.Process.THREAD_PRIORITY_URGENT_AUDIO); recordInstance = new AudioRecord(MediaRecorder.AudioSource.MIC, FREQUENCY, CHANNEL, ENCODING, 8000); recordInstance.startRecording(); short[] tempBuffer = new short[BUFFSIZE]; int retval = 0; while (this.isRunning) { for (int i = 0; i < BUFFSIZE - 1; i++) { tempBuffer[i] = 0; } retval = recordInstance.read(tempBuffer, 0, BUFFSIZE); ... // process the data } This works on the HTC Dream and the HTC Magic perfectly without any log warnings/errors, but causes problems on the emulators and Nexus One device. On the Nexus one, it simply never returns useful data. I cannot provide any other useful information as I'm having a remote friend do the testing. On the emulators (Android 1.5, 2.1 and 2.2), I get weird errors from the AudioFlinger and Buffer overflows with the AudioRecordThread. I also get a major slowdown in UI responsiveness (even though the recording takes place in a separate thread than the UI). Is there something apparent that I'm doing incorrectly? Do I have to do anything special for the Nexus One hardware?

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• Qt application crashing immediately without debugging info. How do I track down the problem?

  - by jjacksonRIAB

  I run an Qt app I've built: ./App Segmentation fault I run it with strace: strace ./App execve("./App", ["./App"], [/* 27 vars */]) = 0 --- SIGSEGV (Segmentation fault) @ 0 (0) --- +++ killed by SIGSEGV +++ Process 868 detached Again, no useful info. I run it with gdb: (gdb) run Starting program: /root/test/App Reading symbols from shared object read from target memory...(no debugging symbols found)...done. Loaded system supplied DSO at 0xffffe000 Program received signal SIGSEGV, Segmentation fault. 0x00000001 in ?? () Again, nothing. I run it with valgrind: ==948== Process terminating with default action of signal 11 (SIGSEGV) ==948== Bad permissions for mapped region at address 0x0 ==948== at 0x1: (within /root/test/App) Even if I put in debugging symbols, it doesn't give any more useful info. ldd shows all libraries being linked properly. Is there any other way I can find out what's wrong? I can't even do standard printf, cout, etc debugging. The executable doesn't even seem to start running at all. I rebuilt with symbols, and tried the suggestion below (gdb) break main Breakpoint 1 at 0x45470 (gdb) run Starting program: /root/test/App Breakpoint 1 at 0x80045470 Reading symbols from shared object read from target memory...done. Loaded system supplied DSO at 0xffffe000 Program received signal SIGSEGV, Segmentation fault. 0x00000001 in ?? () I checked for static initializers and I don't seem to have any. Yep, I tried printf, cout, etc. It doesn't even make it into the main routine, so I'm looking for problems with static initializers in link libraries, adding them in one-by-one. I'm not getting any stack traces either.

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• Micro Second resolution timestamps on windows.

  - by Nikhil

  How to get micro second resolution timestamps on windows? I am loking for something better than QueryPerformanceCounter, QueryPerformanceFrequency (these can only give you an elapsed time since boot, and are not necessarily accurate if they are called on different threads - ie QueryPerformanceCounter may return different results on different CPUs. There are also some processors that adjust their frequency for power saving, which apparently isn't always reflected in their QueryPerformanceFrequency result.) There is this, http://msdn.microsoft.com/en-us/magazine/cc163996.aspx but it does not seem to be solid. This looks great but its not available for download any more. http://www.ibm.com/developerworks/library/i-seconds/ This is another resource. http://www.lochan.org/2005/keith-cl/useful/win32time.html But requires a number of steps, running a helper program plus some init stuff also, I am not sure if it works on multiple CPUs Also looked at the Wikipedia link on the subject which is interesting but not that useful. http://en.wikipedia.org/wiki/Time_Stamp_Counter If the answer is just do this with BSD or Linux, its a lot easier thats fine, but I would like to confirm this and get some explanation as to why this is so hard in windows and so easy in linux and bsd. Its the same damm hardware...

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• Does anyone know of any good open source voting software?

  - by mezoid

  I'm looking for a voting system that we can implement at work amongst our developers. We need something that allows developers to submit ideas about what we can do to improve our development practices (amongst other things) and then have all the developers vote on the ideas to give everyone an idea of what ideas we should attempt to implement first. For example, our developers could list ideas for parts of our code base that should be improved/cleaned up and we'd be able to collectively vote on which parts to start on first. Something like www.uservoice.com might be one way of getting what we need but I'm still wanting to look at alternatives. Unfortunately, googling for voting and polling systems just doesn't seem to bring up any useful results because most of them seem geared towards elections and surveys rather than a way for people to make suggestions and vote on them. Does anyone here know of any sort of software system that might be able to do what I'm looking for? Better yet, does anyone have such a system set up for the developers at their work place? I'd be interested in knowing if it is useful at all.

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• Why doesn't the Java Collections API include a Graph implementation?

  - by dvanaria

  I’m currently learning the Java Collections API and feel I have a good understanding of the basics, but I’ve never understood why this standard API doesn’t include a Graph implementation. The three base classes are easily understandable (List, Set, and Map) and all their implementations in the API are mostly straightforward and consistent. Considering how often graphs come up as a potential way to model a given problem, this just doesn’t make sense to me (it’s possible it does exist in the API and I’m not looking in the right place of course). Steve Yegge suggests in one of his blog posts that a programmer should consider graphs first when attacking a problem, and if the problem domain doesn’t fit naturally into this data structure, only then consider the alternative structures. My first guess is that there is no universal way to represent graphs, or that their interfaces may not be generic enough for an API implementation to be useful? But if you strip down a graph to its basic components (vertices and a set of edges that connect some or all of the vertices) and consider the ways that graphs are commonly constructed (methods like addVertex(v) and insertEdge(v1, v2)) it seems that a generic Graph implementation would be possible and useful. Thanks for helping me understand this better.

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• Using JMX classes to notify on events over time

  - by Cincinnati Joe

  I've been looking at JMX for monitoring application and system metrics (partially because MBeans can accessed by various tools such as JConsole). It would seem like the classes included with JMX would be useful for things like notification when metrics have exceeded thresholds. But I'm not sure they fit with the way I want to measure these over a specified time period. For example, let's say I want to notify an admin when the average CPU load is over 95% for more than 5 minutes. Is that something can be done with a GaugeMonitor? From the docs, it doesn't seem quite suited for this, and I'm wondering if instead I should write my own MBean with the necessary logic. A more relevant example is when the login times for users exceed 10s over a period of 5 mins. Slightly different would be the last 20 logins took more than 10s on average. Another case would be when a process crashes 4+ times in an hour. Or the request queue exceeds 15 for 5 mins. Are the JMX Monitor classes useful for this kind of thing?

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• Good Replacement for User Control?

  - by David Lively

  I found user controls to be incredibly useful when working with ASP.NET webforms. By encapsulating the code required for displaying a control with the markup, creation of reusable components was very straightforward and very, very useful. While MVC provides convenient separation of concerns, this seems to break encapsulation (ie, you can add a control without adding or using its supporting code, leading to runtime errors). Having to modify a controller every time I add a control to a view seems to me to integrate concerns, not separate them. I'd rather break the purist MVC ideology than give up the benefits of reusable, packaged controls. I need to be able to include components similar to webforms user controls throughout a site, but not for the entire site, and not at a level that belongs in a master page. These components should have their own code not just markup (to interact with the business layer), and it would be great if the page controller didn't need to know about the control. Since MVC user controls don't have codebehind, I can't see a good way to do this. I've searched previous SO questions, and have yet to find a good answer. Options so far In an attempt to avoid turning the comments section into a discussion... RenderAction This allows the view to call another controller, which will be responsible for interacting with the BLL and whatever data is necessary to its corresponding view. The calling view needs to be aware of the sub controller. This seems to provide a nice way to encapsulate partial views and controls, without having to modify the calling controller. RenderPartial The calling controller is still responsible for executing whatever code is associated with the partial view, and making sure that the model passed to the partial view contains the data it expects. Effectively, modifying the partial view potentially means modifying the calling controller. Annoying especially if this is used in multiple places. Portable Areas Place each control in its own project/area?

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• Evaluating expressions using Visual Studio 2005 SDK rather than automation's Debugger::GetExpression

  - by brone

  I'm looking into writing an addin (or package, if necessary) for Visual Studio 2005 that needs watch window type functionality -- evaluation of expressions and examination of the types. The automation facilities provide Debugger::GetExpression, which is useful enough, but the information provided is a bit crude. From looking through the docs, it sounds like an IDebugExpressionContext2 would be more useful. With one of these it looks as if I can get more information from an expression -- detailed information about the type and any members and so on and so forth, without having everything come through as strings. I can't find any way of actually getting a IDebugExpressionContext2, though! IDebugProgramProvider2 sort of looks relevant, in that I could start with IDebugProgramProvider2::GetProviderProcessData and then slowly drill down until reaching something that can supply my expression context -- but I'll need to supply a port to this, and it's not clear how to retrieve the port corresponding to the current debug session. (Even if I tried every port, it's not obvious how to tell which port is the right one...) I'm becoming suspicious that this simply isn't a supported use case, but with any luck I've simply missed something crashingly obvious. Can anybody help?

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• Design by contracts and constructors

  - by devoured elysium

  I am implementing my own ArrayList for school purposes, but to spice up things a bit I'm trying to use C# 4.0 Code Contracts. All was fine until I needed to add Contracts to the constructors. Should I add Contract.Ensures() in the empty parameter constructor? public ArrayList(int capacity) { Contract.Requires(capacity > 0); Contract.Ensures(Size == capacity); _array = new T[capacity]; } public ArrayList() : this(32) { Contract.Ensures(Size == 32); } I'd say yes, each method should have a well defined contract. On the other hand, why put it if it's just delegating work to the "main" constructor? Logicwise, I wouldn't need to. The only point I see where it'd be useful to explicitly define the contract in both constructors is if in the future we have Intelisense support for contracts. Would that happen, it'd be useful to be explicit about which contracts each method has, as that'd appear in Intelisense. Also, are there any books around that go a bit deeper on the principles and usage of Design by Contracts? One thing is having knowledge of the syntax of how to use Contracts in a language (C#, in this case), other is knowing how and when to use it. I read several tutorials and Jon Skeet's C# in Depth article about it, but I'd like to go a bit deeper if possible. Thanks

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• Capturing output of find . -print0 into a bash array

  - by Idris

  Using find . -print0 seems to be the only safe way of obtaining a list of files in bash due to the possibility of filenames containing spaces, newlines, quotation marks etc. However, I'm having a hard time actually making find's output useful within bash or with other command line utilities. The only way I have managed to make use of the output is by piping it to perl, and changing perl's IFS to null: find . -print0 | perl -e '$/="\0"; @files=<>; print $#files;' This example prints the number of files found, avoiding the danger of newlines in filenames corrupting the count, as would occur with: find . | wc -l As most command line programs do not support null-delimited input, I figure the best thing would be to capture the output of find . -print0 in a bash array, like I have done in the perl snippet above, and then continue with the task, whatever it may be. How can I do this? This doesn't work: find . -print0 | ( IFS=$'\0' ; array=( $( cat ) ) ; echo ${#array[@]} ) A much more general question might be: How can I do useful things with lists of files in bash?

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• java - question about thread abortion and deadlock - volatile keyword

  - by Tiyoal

  Hello all, I am having some troubles to understand how I have to stop a running thread. I'll try to explain it by example. Assume the following class: public class MyThread extends Thread { protected volatile boolean running = true; public void run() { while (running) { synchronized (someObject) { while (someObject.someCondition() == false && running) { try { someObject.wait(); } catch (InterruptedException e) { e.printStackTrace(); } } // do something useful with someObject } } } public void halt() { running = false; interrupt(); } } Assume the thread is running and the following statement is evaluated to true: while (someObject.someCondition() == false && running) Then, another thread calls MyThread.halt(). Eventhough this function sets 'running' to false (which is a volatile boolean) and interrupts the thread, the following statement is still executed: someObject.wait(); We have a deadlock. The thread will never be halted. Then I came up with this, but I am not sure if it is correct: public class MyThread extends Thread { protected volatile boolean running = true; public void run() { while (running) { synchronized (someObject) { while (someObject.someCondition() == false && running) { try { someObject.wait(); } catch (InterruptedException e) { e.printStackTrace(); } } // do something useful with someObject } } } public void halt() { running = false; synchronized(someObject) { interrupt(); } } } Is this correct? Is this the most common way to do this? This seems like an obvious question, but I fail to come up with a solution. Thanks a lot for your help.

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• Why does mobile first responsive design tend to not use max-width queries alongside the min-width queries?

  - by Sam

  First off, I understand the basic principles behind mobile first responsive web design, and totally agree with them. But one thing I don't understand: In my experience, not all styles for small screens can be used for the larger version of a website. For example, usually smaller versions tend to have larger clickable areas, hamburger navigation, etc. So I sometimes have to override these specific styles, aside from just progressively enhancing the base styles. So I was wondering: why is max-width rarely mentioned (or used) in the context of mobile-first responsive web design? Because it looks like it could be used to isolate styles for smaller screens that are not useful for larger screens, and would thus prevent unnecessary duplication of code. A quote which mentions min-width as typically mobile-first, but not max-width: Mobile first, from a coding perspective, means that your base style is typically a single-column, fully-fluid layout. You use @media (min-width: whatever) to add a grid-based layout on top of that. from: http://gomakethings.com/mobile-first-and-internet-explorer/ EDIT: So to be more specific: I was wondering if there is a reason to exclude max-width from a mobile-first responsive design (as it seems like it can be useful for writing your css as DRY as possible, as some styles for small screens will not be used for bigger screens).

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• 2d Game Making > Where can someone get Free Tilesets?

  - by Iscariot

  I have been scouring the internet for free tilesets that are open to you. I have found http://lostgarden.com/ It does not seem very useful. There are a few things here and there, but overall not much to really make a game off of. http://www.flyingyogi.com/fun/spritelib.html Spritelib is a little better it has some useful information, but is still the graphics are more in the 8bit variety. http://reinerstileset.4players.de/ This is heavily stylized and its hard to have this match with any other free tile-sets available. All other sites I have found have just been rips from games and those are protected by a copyright and remain unusable. Right now I need simple objects to build the inside of buildings, but I have seem to have come up short in that area. I have plenty of things for outside of buildings, but nothing for in. I am hoping someone else has had this problem and has found a solution. If not, I hope the information I have provided can help someone else in their conquest.

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• Why can a public class not inherit from a less visible one?

  - by Dan Tao

  I apologize if this question has been asked before. I've searched SO somewhat and wasn't able to find it. I'm just curious what the rationale behind this design was/is. Obviously I understand that private/internal members of a base type cannot, nor should they, be exposed through a derived public type. But it seems to my naive thinking that the "hidden" parts could easily remain hidden while some base functionality is still shared and a new interface is exposed publicly. I'm thinking of something along these lines: Assembly X internal class InternalClass { protected virtual void DoSomethingProtected() { // Let's say this method provides some useful functionality. // Its visibility is quite limited (only to derived types in // the same assembly), but at least it's there. } } public class PublicClass : InternalClass { public void DoSomethingPublic() { // Now let's say this method is useful enough that this type // should be public. What's keeping us from leveraging the // base functionality laid out in InternalClass's implementation, // without exposing anything that shouldn't be exposed? } } Assembly Y public class OtherPublicClass : PublicClass { // It seems (again, to my naive mind) that this could work. This class // simply wouldn't be able to "see" any of the methods of InternalClass // from AssemblyX directly. But it could still access the public and // protected members of PublicClass that weren't inherited from // InternalClass. Does this make sense? What am I missing? }

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• Ways to support manually executed tests? (that can be used on a Mac)

  - by Rinzwind

  Are there any tools that can be used on a Mac to support manually executed tests? I have a number of tests that I'm executing manually and which I'm currently documenting using merely a plain text file. "Tools" can be interpreted rather loosely here, anything that's a step up from the plain text file would be useful: a template for some suitable application, supporting AppleScript scripts, a web-based system, a full-blown application ... Some things that would be great to have better support for (see also the example below): Checking off each step while you're manually executing the test. Showing the next step(s) in a small window that is always kept in front of all other windows. Automatically updating the 'last tested' and 'using svn revision' info. Keeping a record of all previous testing rounds (not just the last one). ... Any suggestions for any such "tools" that can be used on a Mac? An example (faked) entry from the plain text file to give you a better idea of what I'm looking for: - Check that exported web pages render properly in Safari. Last tested: 2010-03-24 Using SVN revision: 1000 Steps: - Open a new document. - Add some items to the document. - Export the document to a web page "Test.html" in a new folder "Export Test" on the Desktop. - Open the web page in Safari, script: tell application "Finder" open file "Test.html" of folder "Export Test" of desktop end tell Expected results: - The web page should appear properly with all items shown. Clean up steps: - Remove the folder "Export Test" from the Desktop. ( Note: for those unaware, the snippet of AppleScript in the above can be executed from most text editing applications through the Services menu by selecting the snippet and using: the application menu Services Script Editor Run as AppleScript. This is quite useful to automate some steps for tests that are difficult to automate as a whole. )

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• Minimal framework in Scala for collections with inheriting return type

  - by Rex Kerr

  Suppose one wants to build a novel generic class, Novel[A]. This class will contain lots of useful methods--perhaps it is a type of collection--and therefore you want to subclass it. But you want the methods to return the type of the subclass, not the original type. In Scala 2.8, what is the minimal amount of work one has to do so that methods of that class will return the relevant subclass, not the original? For example, class Novel[A] /* What goes here? */ { /* Must you have stuff here? */ def reverse/* What goes here instead of :Novel[A]? */ = //... def revrev/*?*/ = reverse.reverse } class ShortStory[A] extends Novel[A] /* What goes here? */ { override def reverse: /*?*/ = //... } val ss = new ShortStory[String] val ss2 = ss.revrev // Type had better be ShortStory[String], not Novel[String] Does this minimal amount change if you want Novel to be covariant? (The 2.8 collections do this among other things, but they also play with return types in more fancy (and useful) ways--the question is how little framework one can get away with if one only wants this subtypes-always-return-subtypes feature.)

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• How is covariance cooler than polymorphism...and not redundant?

  - by P.Brian.Mackey

  .NET 4 introduces covariance. I guess it is useful. After all, MS went through all the trouble of adding it to the C# language. But, why is Covariance more useful than good old polymorphism? I wrote this example to understand why I should implement Covariance, but I still don't get it. Please enlighten me. using System; using System.Collections.Generic; using System.Linq; using System.Text; namespace Sample { class Demo { public delegate void ContraAction<in T>(T a); public interface IContainer<out T> { T GetItem(); void Do(ContraAction<T> action); } public class Container<T> : IContainer<T> { private T item; public Container(T item) { this.item = item; } public T GetItem() { return item; } public void Do(ContraAction<T> action) { action(item); } } public class Shape { public void Draw() { Console.WriteLine("Shape Drawn"); } } public class Circle:Shape { public void DrawCircle() { Console.WriteLine("Circle Drawn"); } } public static void Main() { Circle circle = new Circle(); IContainer<Shape> container = new Container<Circle>(circle); container.Do(s => s.Draw());//calls shape //Old school polymorphism...how is this not the same thing? Shape shape = new Circle(); shape.Draw(); } } }

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• Things to Avoid in C/C++ [closed]

  - by piemesons

  Possible Duplicate: What C++ pitfalls should I avoid ? While searching for some information, I stumbled upon this series of small articles, Things to avoid in C/C++. So, thought of sharing it... "C/C++ programmers are allowed to do some things they shouldn't. We are given functions that are supposed to be useful but aren't because of hidden faults, or taught ways to do things that are bad, wrong, not necessary. These posts will discuss many of these as time goes on." gets(): http://www.gidnetwork.com/b-56.html fflush(stdin): http://www.gidnetwork.com/b-57.html feof(): http://www.gidnetwork.com/b-58.html system("PAUSE"): http://www.gidnetwork.com/b-61.html scanf: http://www.gidnetwork.com/b-59.html scanf / character: http://www.gidnetwork.com/b-60.html scanf / string: http://www.gidnetwork.com/b-62.html scanf / number: http://www.gidnetwork.com/b-63.html scanf / epilogue: http://www.gidnetwork.com/b-64.html void main(): http://www.gidnetwork.com/b-66.html As this is a very useful subject/topic, I request all the members to keep adding valuable information to this thread, and make it a good source of information for all level of programmers, especially for beginners. Thanks...

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