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• Why can't I project ToString() in VB?

  - by Martinho Fernandes

  If you try to compile the query below in Visual Basic .NET, it fails. From x In {1, 2} Select x.ToString() The error given by the compiler is: Range variable name cannot match the name of a member of the 'Object' class. There is nothing wrong with the equivalent C# query, though: from x in new[]{1, 2} select x.ToString() This does not happen with the ToString overload that takes a format (it is a member of Int32, not Object). It does happen with other members of Object, as long as they don't take an argument: with GetType and GetHashCode it fails; with Equals(object) it compiles. Why is this restriction in place, and what alternatives can I use?

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• assignment from incompatible pointer type

  - by Hristo

  I have set up the following struct: typedef struct _thread_node_t { pthread_t thread; struct thread_node_t *next; } thread_node_t; ... and then I have defined: // create thread to for incoming connection thread_node_t *thread_node = (thread_node_t*) malloc(sizeof(thread_node_t)); pthread_create(&(thread_node->thread), NULL, client_thread, &csFD); thread_node->next = thread_arr; // assignment from incompatible pointer type thread_arr = thread_node; where thread_arr is thread_node_t *thread_arr = NULL; I don't understand why the compiler is complaining. Maybe I'm misunderstanding something.

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• Can a method return an NSRange?

  - by Dan Donaldson

  I have a method that returns an NSRange. When I call this method from outside the class I get a compile error. NSRange tmpRange; tmpRange = [phrase rangeInString:searchString forString:theLetter goingForward:YES]; return tmpRange.location == -1; in the .h file: #import <Foundation/Foundation.h> @interface Phrase : NSObject { } - (NSRange) rangeInString:(NSString *) tgt forString:(NSString *) find goingForward:(BOOL) fwd; @end This method is called within the Phrase object by other methods without problems. The compiler says 'incompatible types in assignment'. Can anyone explain this to me? I assume it has to do with returning an NSRange/struct type value generated outside the object, but I don't know why it works in one place and not the other.

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• SEO on a login based website

  - by Paul

  Ok so say I have a website that the majority of content is behind a closed door, login screen for paying customers only. How can I let google know what is there so people can find the site through a search engine. What programming techniques could I use to give more content to the google bot. I will have some overview and demonstration screens to tempt the users but will these five to ten pages of content be enough for the search engines. The key work is quite a highly sort one and there is quite alot of competition. And before anyone asks the site is not a subscription porn site (Sadly)

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• Create object of unknown class (two inherited classes)

  - by Paul

  I've got the following classes: class A { void commonFunction() = 0; } class Aa: public A { //Some stuff... } class Ab: public A { //Some stuff... } Depending on user input I want to create an object of either Aa or Ab. My imidiate thought was this: A object; if (/*Test*/) { Aa object; } else { Ab object; } But the compiler gives me: error: cannot declare variable ‘object’ to be of abstract type ‘A’ because the following virtual functions are pure within ‘A’: //The functions... Is there a good way to solve this?

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• Pattern matching against Scala Map type

  - by Tom Morris

  Imagine I have a Map[String, String] in Scala. I want to match against the full set of key–value pairings in the map. Something like this ought to be possible val record = Map("amenity" -> "restaurant", "cuisine" -> "chinese", "name" -> "Golden Palace") record match { case Map("amenity" -> "restaurant", "cuisine" -> "chinese") => "a Chinese restaurant" case Map("amenity" -> "restaurant", "cuisine" -> "italian") => "an Italian restaurant" case Map("amenity" -> "restaurant") => "some other restaurant" case _ => "something else entirely" } The compiler complains thulsy: error: value Map is not a case class constructor, nor does it have an unapply/unapplySeq method What currently is the best way to pattern match for key–value combinations in a Map?

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• How do you get GWT 2.0 to accept clicks on two different Widgets added to a LayoutPanel?

  - by kerrr

  Using GWT 2.0 I have an entry point that adds two Widgets to a LayoutPanel. The Widgets both handle click events and have click events ergistered to them. The problem is that only the last widget added to the LayoutPanel can actually be clicked. Switch the order in which the widgets are added switches the widget that works. Add mroe widgets and still the only you can click is the last one added to the LayoutPanel. Any idea why this is? Is there any reasoning behind the behaviour, or have I missunderstood what is happening under the covers? How do I gat all widgets in the LayoutPanel to accept events? Should I be using another panel class? I'm not too bothered if the LayoutPanel prevents anything below it from being clicked, but want all Widgets added to it to be clickable.

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• How to use git to download a particular tag?

  - by Jack BeNimble

  I'm trying to figure out how do download a particular tag of a git repository - it's one version behind the current version. I saw there was a tag for the previous version on the git web page, with object name of something long hex number. But the version name is "Tagged release 1.1.5" according the site. I tried a command like this (with names changed): git clone http://git.abc.net/git/abc.git my_abc And I did get something - a directory, a bunch of subdirectories, etc. If it's the whole repository, how do I get at the version I'm seeking? If not, how do I download that particular version?

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• Is there a TextWriter interface to the System.Diagnostics.Debug class?

  - by John Källén

  I'm often frustrated by the System.Diagnostics.Debug.Write/WriteLine methods. I would like to use the Write/WriteLine methods familiar from the TextWriter class, so I often write Debug.WriteLine("# entries {0} for connection {1}", countOfEntries, connection); which causes a compiler error. I end up writing Debug.WriteLine(string.Format("# entries {0} for connection {1}", countOfEntries, connection)); which is really awkward. Does the CLR have a class deriving from TextWriter that "wraps" System.Debug, or should I roll my own?

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• hook to save action in eclipse plugin

  - by 4485670

  I want to create a Google Closure Compiler plugin for eclipse. I already have a popup menu entry to compile a Javascript file to its minified version. But it would be more than helpful if every time you save a *.js that minified version would be generated automatically. I read/heard about natures and builders, extension points and IResourceChangeListener. But I did not manage to figure out what I should use and especially how to get it to work. Is there a working example of a plugin that does "the same kind of thing" so I can work from that or a tutorial to write such? With the answer below I searched for projects that use the IResourceChangeListener and came up with this code: manifest: http://codepaste.net/3yahwe plugin.xml: http://codepaste.net/qek3rw activator: http://codepaste.net/s7xowm DummyStartup: http://codepaste.net/rkub82 MinifiedJavascriptUpdater: http://codepaste.net/koweuh There in the MinifiedJavascriptUpdater.java which holds the code for the IResourceChangeListener the "resourceChanged" function is never reached.

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• Why do you sometimes need to write <typename T> instead of just <T> ?

  - by StackedCrooked

  I was reading the Wikipedia article on SFINAE and encountered following code sample: struct Test { typedef int Type; }; template < typename T > void f( typename T::Type ) {} // definition #1 template < typename T > void f( T ) {} // definition #2 void foo() { f< Test > ( 10 ); //call #1 f< int > ( 10 ); //call #2 without error thanks to SFINAE } Now I've actually written code like this before, and somehow intuitively I knew that I needed to type "typename T" instead of just "T". However, it would be nice to know the actual logic behind it. Anyone care to explain?

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• Assigning Value to a variable that is too big for it! (checked and unchecked concept)

  - by ThickBook

  So when we assign a value to a variable then that variable should be able to hold it, right? and if not compiler produces the error. Now there is an option in C# known as Checked (which is by default) and unchecked option. But is there practical use of unchecked? any comments for a layman? :) Example: int a=int.MaxValue; int b=int.MaxValue; unchecked { int sum=a+b; }

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• Will Haskell be a good choice for my task?

  - by Narzanka

  I'm starting a new project and don't know which language to use. My 'must have' requirements are: Be able to run on Windows/LinuxMacOs natively (native executable) - user should be able to just run the exe (when on Windows for example) and see the results. No runtimes/interpreters (no jvm, clr, etc) - one file download should be enough to run the application. Full unicode support. Be able to manipulate OS threads (create them, run multiple tasks in parallel on multi-core CPUs, etc). Be reasonably fast (Python level performance and better). To have some kind of standard library that does low-level, mundane tasks. Not very niche and have some community behind it to be able to ask questions. My 'nice to have' requirements are: Language should be functional It should have good string manipulation capabilities (not necessarily regex) Not extremely hard to learn I'm thinking about Haskell now but keeping in mind OCaml as well. Please advice if my choice is correct.

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• Pointer aliasing- in C++0x

  - by DeadMG

  I'm thinking about (just as an idea) disjointed pointer aliasing in C++0x. I was thinking about seeing if it could be implemented similarly to const correctness- that is, enforced by the compiler. What would be the requirements for such a thing? As this is more of a thought experiment, I'm perfectly happy to look at solutions that destroy legacy code or redefine half the language and that kind of thing. What I'd really rather not do is have, say, restrict from C99 where the programmer just promises it. It should be enforced.

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• getElementById does return null

  - by pbcoder

  I have following function: $('canvas').createWindow('xyz', 500, 600); And js-code behind is: var $ = function(element) { if (this.constructor !== $) { return new $(element); } alert(element); var windowObj = document.getElementById(element); this.createWindow = function(src, width, height) { if(width != "" && height != "") { windowWidth = windowObj.style.width = width + 'px'; windowHeight = windowObj.style.height = height + 'px'; } }; }; But the problem is that JS says windowObj is null, alert(element) works fine! Thanks for your help!

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• Can I reproduce Scala's behavior for == ?

  - by JPP

  In Programming in Scala, I can read that the == operator behaves as if it was defined like this: final def == (that: Any): Boolean = if (null eq this) {null eq that} else {this equals that} But there must actually be compiler magic to avoid null pointer exceptions, right? Is there any way for me to replicate this behavior with pure Scala; i.e., have an operator/method return one thing if the receiver is null and another one if it isn't? What I mean is an actual implementation of null eq this. I suppose I can write a "pimp" and then define the method on the wrapper class, but is there a more direct way to do this?

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• Same memory space being allocated again & again

  - by shadyabhi

  In each loop iteration, variable j is declared again and again. Then why is its address remaining same? Shouldn't it be given some random address each time? Is this compiler dependent? #include<stdio.h> #include<malloc.h> int main() { int i=3; while (i--) { int j; printf("%p\n", &j); } return 0; } Testrun:- shadyabhi@shadyabhi-desktop:~/c$ gcc test.c shadyabhi@shadyabhi-desktop:~/c$ ./a.out 0x7fffc0b8e138 0x7fffc0b8e138 0x7fffc0b8e138 shadyabhi@shadyabhi-desktop:~/c$

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• How does * work in Python

  - by Deqing

  Just switched from C++ to Python, and found that sometimes it is a little hard to understand ideas behind Python. I guess, a variable is a reference to the real object. For example, a=(1,2,5) meaning a - (1,2,5), so if b=a, then b and a are 2 references pointing to the same (1,2,5). It is a little like pointers in C/C++. If I have: def foo(a,b,c): print a,b,c a=(1,3,5) foo(*a) What does * mean here? Looks like it expands tuple a to a[0], a[1] and a[2]. But why print(*a) is not working while print(a[0],a[1],a[2]) works fine?

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• c++ - FIFO implementation

  - by Narek

  While implementing a FIFO I have used the following structure: struct Node { T info_; Node* link_; Node(T info, Node* link=0): info_(info), link_(link) {} }; I think this a well known trick for lots of STL containers (for example for List). Is this a good practice? What it means for compiler when you say that Node has a member with a type of it's pointer? Is this a kind of infinite loop? And finally, if this is a bad practice, how I could implement a better FIFO.

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• how to specify a pointer to an overloaded function?

  - by davka

  I want to pass an overloaded function to the std::for_each() algorithm. e.g.: void f(char c); void f(int i); std::string s("example"); std::for_each(s.begin(), s.end(), f); I'd expect the compiler to resolve f() by the iterator type. Apparently, it (gcc 4.1.2) doesn't do it. So, how can I specify which f() I want? thanks a lot

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• Inter-project dependencies

  - by Mike Hordecki

  Hello! I'm doing some Delphi (2010) work this summer, and I've stumbled upon this problem: My project consists of reusable backend library and a bunch of GUIs that tap into its interface. In this circumstances I've decided to make the backend and GUIs separate projects within single project group (I hope my train of thought is correct). The problem is, how can I include units from the backend in a GUI project? I've tried to modify Project Options > Directories and Conditionals but compiler still complains about being unable to find proper .dcu's. Any ideas? Your help will be appreciated.

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• How to map an property of ClassA to one of SuperclassA?

  - by mystify

  I have a class named SuperclassA, and an class named ClassA. ClassA inherits from SuperclassA. SuperclassA has got an property called something, so a very generic not-much-saying name. In ClassA, I want to have an property which maps to that something of SuperclassA. How could I do that? I want to make absolutely sure that any access to myBetterProperty results in accessing what's behind something. Assigning an value to myBetterProperty should result in assigning one to something, and vice versa. How to? Pointers set up in init? How would that look like? *self.myBetterProperty = &something; ? I'm not sure about that...

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• Java concurrency - Should block or yield?

  - by teto

  Hi, I have multiple threads each one with its own private concurrent queue and all they do is run an infinite loop retrieving messages from it. It could happen that one of the queues doesn't receive messages for a period of time (maybe a couple seconds), and also they could come in big bursts and fast processing is necessary. I would like to know what would be the most appropriate to do in the first case: use a blocking queue and block the thread until I have more input or do a Thread.yield()? I want to have as much CPU resources available as possible at a given time, as the number of concurrent threads may increase with time, but also I don't want the message processing to fall behind, as there is no guarantee of when the thread will be reescheduled for execution when doing a yield(). I know that hardware, operating system and other factors play an important role here, but setting that aside and looking at it from a Java (JVM?) point of view, what would be the most optimal?

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• Is new int[10]() valid c++?

  - by Naveen

  While trying to answer this question I found that the code int* p = new int[10](); compiles fine with VC9 compiler and initializes the integers to 0. So my questions are: First of all is this valid C++ or is it a microsoft extension? Is it guaranteed to initialize all the elements of the array? Also, is there any difference if I do new int; or new int();? Does the latter guarantee to initialize the variable?

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• Why does Generic class signature requires specifying new() if type T needs instantiation ?

  - by this. __curious_geek

  I'm writing a Generic class as following. public class Foo<T> : where T : Bar, new() { public void MethodInFoo() { T _t = new T(); } } As you can see the object(_t) of type T is instantiated at run-time. To support instantiation of generic type T, language forces me to put new() in the class signature. I'd agree to this if Bar is an abstract class but why does it need to be so if Bar standard non-abstract class with public parameter-less constructor. compiler prompts following message if new() is not found. Cannot create an instance of the variable type 'T' because it does not have the new() constraint

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