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  • C# - closures over class fields inside an initializer?

    - by Richard Berg
    Consider the following code: using System; namespace ConsoleApplication2 { class Program { static void Main(string[] args) { var square = new Square(4); Console.WriteLine(square.Calculate()); } } class MathOp { protected MathOp(Func<int> calc) { _calc = calc; } public int Calculate() { return _calc(); } private Func<int> _calc; } class Square : MathOp { public Square(int operand) : base(() => _operand * _operand) // runtime exception { _operand = operand; } private int _operand; } } (ignore the class design; I'm not actually writing a calculator! this code merely represents a minimal repro for a much bigger problem that took awhile to narrow down) I would expect it to either: print "16", OR throw a compile time error if closing over a member field is not allowed in this scenario Instead I get a nonsensical exception thrown at the indicated line. On the 3.0 CLR it's a NullReferenceException; on the Silverlight CLR it's the infamous Operation could destabilize the runtime.

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  • How to avoid code repetition initializing final properties?

    - by Hernán Eche
    public class Code{ //many properties //... final String NEWLINE;// ohh a final property! void creation() //this method is for avoid repetition of code { //final initialization can't be put here =( Source= new StringBuffer(); //many other commons new's .. //... } Code() { NEWLINE = System.getProperty("line.separator"); creation(); } Code(String name, int numberr) { NEWLINE = System.getProperty("line.separator"); creation(); name=new Someting(name); number = new Magic(number); } }

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  • What is the difference among NSString alloc:initWithCString versus stringWithUTF8String?

    - by mobibob
    I thought these two methods were (memory allocation-wise) equivalent, however, I was seeing "out of scope" and "NSCFString" in the debugger if I used what I thought was the convenient method (commented out below) and when I switched to the more explicit method my code stopped crashing! Notice that I am getting the string that is being stored in my container from sqlite3 query. p = (char*) sqlite3_column_text (queryStmt, 1); // GUID = (NSString*) [NSString stringWithUTF8String: (p!=NULL) ? p : ""]; GUID = [[NSString alloc] initWithCString:(p!=NULL) ? p : "" encoding:NSUTF8StringEncoding]; Also note, that if I looked at the values in the debugger and printed them with NSLog they looked correct, however, I don't think new memory was allocated and the value copied. Instead the memory pointer was stored - went out of scope - referenced later - crash!

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  • Java - Should private instance variables be accessed in constructors through getters and setters met

    - by Yatendra Goel
    I know that private instance variables are accessed through their public getters and setters method. But when I generate constructors with the help of IDE, it initializes instance variables directly instead of initializing them through their setter methods. Q1. So should I change the IDE generated code for constructors to initialize those instance variables through their setter methods. Q2. If yes, then why IDE don't generate constructors code in that way?

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  • 'Set = new HashSet' or 'HashSet = new Hashset'?

    - by Pureferret
    I'm intialising a HashSet like so in my program: Set<String> namesFilter = new HashSet<String>(); Is this functionally any different if I initilise like so? HashSet<String> namesFilter = new HashSet<String>(); I've read this about the collections interface, and I understand interfaces (well, except their use here). I've read this excerpt from Effective Java, and I've read this SO question, but I feel none the wiser. Is there a best practice in Java, and if so, why? My intuition is that it makes casting to a different type of Set easier in my first example. But then again, you'd only be casting to something that was a collection, and you could convert it by re-constructing it.

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  • Vague MVC and Castle Windsor question. Sorry...

    - by Matt W
    I have inheritted some code in which the MVC Controller classes all get their constructors called by Castle....DefaultProxyFactory.Create() somewhere along the line (the call stack drops out to the , which isn't helping.) So, basically, how would I go about finding out where Castle is being told how to call the constructors of my Controllers? I am very new to Castle, Windsor and MicroKernel, etc, and not a master of ASP's MVC. Many thanks for any pointers - sorry about the vagueness, Matt.

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  • toString method for varargs contructor

    - by owca
    I have a varargs contructor like this : public class Sentence { public String[] str; public Sentence(Object... text){ StringBuilder sb = new StringBuilder(); for (Object o : text) { sb.append(o.toString()) .append(" "); } System.out.println(sb.toString()); } } Contructor can get various types of data (ints, strings, and Sentence objects as well). How to do a proper toString method for such class ?

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  • How to write a cctor and op= for a factory class with ptr to abstract member field?

    - by Kache4
    I'm extracting files from zip and rar archives into raw buffers. I created the following to wrap minizip and unrarlib: Archive.hpp #include "ArchiveBase.hpp" #include "ArchiveDerived.hpp" class Archive { public: Archive(string path) { /* logic here to determine type */ switch(type) { case RAR: archive_ = new ArchiveRar(path); break; case ZIP: archive_ = new ArchiveZip(path); break; case UNKNOWN_ARCHIVE: throw; break; } } Archive(Archive& other) { archive_ = // how do I copy an abstract class? } ~Archive() { delete archive_; } void passThrough(ArchiveBase::Data& data) { archive_->passThrough(data); } Archive& operator = (Archive& other) { if (this == &other) return *this; ArchiveBase* newArchive = // can't instantiate.... delete archive_; archive_ = newArchive; return *this; } private: ArchiveBase* archive_; } ArchiveBase.hpp class ArchiveBase { public: // Is there any way to put this struct in Archive instead, // so that outside classes instantiating one could use // Archive::Data instead of ArchiveBase::Data? struct Data { int field; }; virtual void passThrough(Data& data) = 0; /* more methods */ } ArchiveDerived.hpp "Derived" being "Zip" or "Rar" #include "ArchiveBase.hpp" class ArchiveDerived : public ArchiveBase { public: ArchiveDerived(string path); void passThrough(ArchiveBase::Data& data); private: /* fields needed by minizip/unrarlib */ // example zip: unzFile zipFile_; // example rar: RARHANDLE rarFile_; } ArchiveDerived.cpp #include "ArchiveDerived.hpp" ArchiveDerived::ArchiveDerived(string path) { //implement } ArchiveDerived::passThrough(ArchiveBase::Data& data) { //implement } Somebody had suggested I use this design so that I could do: Archive archiveFile(pathToZipOrRar); archiveFile.passThrough(extractParams); // yay polymorphism! How do I write a cctor for Archive? What about op= for Archive? What can I do about "renaming" ArchiveBase::Data to Archive::Data? (Both minizip and unrarlib use such structs for input and output. Data is generic for Zip & Rar and later is used to create the respective library's struct.)

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  • Using "Object.create" instead of "new"

    - by Graham King
    Javascript 1.9.3 / ECMAScript 5 introduces Object.create, which Douglas Crockford amongst others has been advocating for a long time. How do I replace new in the code below with Object.create? var UserA = function(nameParam) { this.id = MY_GLOBAL.nextId(); this.name = nameParam; } UserA.prototype.sayHello = function() { console.log('Hello '+ this.name); } var bob = new UserA('bob'); bob.sayHello(); (Assume MY_GLOBAL.nextId exists). The best I can come up with is: var userB = { init: function(nameParam) { this.id = MY_GLOBAL.nextId(); this.name = nameParam; }, sayHello: function() { console.log('Hello '+ this.name); } }; var bob = Object.create(userB); bob.init('Bob'); bob.sayHello(); There doesn't seem to be any advantage, so I think I'm not getting it. I'm probably being too neo-classical. How should I use Object.create to create user 'bob'?

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  • optional arguments in haskell

    - by snorlaks
    Hello, I have declared my own type: data Book = Bookinfo { bookId :: Int, title :: String } deriving(Show) and now: x = Bookinfo it is all ok, valid statement but making bookId x throws an error. If I would be able to handle errors in Haskell that would be ok but right now I cant do this So Im curious how to make not specified values of fields take default value, and what exactly value is there when I'm not giving vcalues of fields in construcotr ? thanks for help

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  • C++ LNK2019 error with constructors and destructors in derived classes

    - by BLH
    I have two classes, one inherited from the other. When I compile, I get the following errors: 1Entity.obj : error LNK2019: unresolved external symbol "public: __thiscall Utility::Parsables::Base::Base(void)" (??0Base@Parsables@Utility@@QAE@XZ) referenced in function "public: __thiscall Utility::Parsables::Entity::Entity(void)" (??0Entity@Parsables@Utility@@QAE@XZ) 1Entity.obj : error LNK2019: unresolved external symbol "public: virtual __thiscall Utility::Parsables::Base::~Base(void)" (??1Base@Parsables@Utility@@UAE@XZ) referenced in function "public: virtual __thiscall Utility::Parsables::Entity::~Entity(void)" (??1Entity@Parsables@Utility@@UAE@XZ) 1D:\Programming\Projects\Caffeine\Debug\Caffeine.exe : fatal error LNK1120: 2 unresolved externals I really can't figure out what's going on.. can anyone see what I'm doing wrong? I'm using Visual C++ Express 2008. Here are the files.. "include/Utility/Parsables/Base.hpp" #ifndef CAFFEINE_UTILITY_PARSABLES_BASE_HPP #define CAFFEINE_UTILITY_PARSABLES_BASE_HPP namespace Utility { namespace Parsables { class Base { public: Base( void ); virtual ~Base( void ); }; } } #endif //CAFFEINE_UTILITY_PARSABLES_BASE_HPP "src/Utility/Parsables/Base.cpp" #include "Utility/Parsables/Base.hpp" namespace Utility { namespace Parsables { Base::Base( void ) { } Base::~Base( void ) { } } } "include/Utility/Parsables/Entity.hpp" #ifndef CAFFEINE_UTILITY_PARSABLES_ENTITY_HPP #define CAFFEINE_UTILITY_PARSABLES_ENTITY_HPP #include "Utility/Parsables/Base.hpp" namespace Utility { namespace Parsables { class Entity : public Base { public: Entity( void ); virtual ~Entity( void ); }; } } #endif //CAFFEINE_UTILITY_PARSABLES_ENTITY_HPP "src/Utility/Parsables/Entity.cpp" #include "Utility/Parsables/Entity.hpp" namespace Utility { namespace Parsables { Entity::Entity( void ) { } Entity::~Entity( void ) { } } }

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  • VB Classes Best Practice - give all properties values?

    - by Becky Franklin
    Sorry if this is a bit random, but is it good practice to give all fields of a class a value when the class is instanciated? I'm just wondering if its better practice to have a constuctor that takes no parameters and gives all the fields default values, or whether fields that have values should be assigned and others left alone until required? I hope that makes sense, Becky

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  • std::string x(x);

    - by FredOverflow
    std::string x(x); This crashes very badly on my compiler. Does this mean I should test for this != &that in my own copy constructors, or can I assume that no client will ever be so stupid?

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  • C# Custom data type!

    - by Betamoo
    After I decided at last to implement my Int128 in C#, I thought it would be nice to make it look like other dotNet data types.. But I could not implement the following feature: suffix initialization: such as 13L and 0.2D Can I make my own suffix in C#? And if I can not.. how can I initialize it? i.e Int128 a= ??

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  • BLL returning the right Type of an instance

    - by Younes
    I have a class "Artikel" and there i write some Business Logic. I also have a class "tArtikel" which is a type. In my class "Artikel" I work with "tArtikel" and returns are of that type. Now when i instantiate an "Artikel" i want it to be of type "tArtikel", so what i tried in my code is: public tArtikel Artikel() { tArtikel artikel = new tArtikel(); } Which results in: "'Artikel' member names cannot be the same as their enclosing type". How would i set this up correctly?

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  • ArgumentError: Error #1063: Argument count mismatch on com.flashden::MenuItem(). Expected 1, got 0.

    - by Suzanne
    I keep getting the below error only in firefox ArgumentError: Error #1063: Argument count mismatch on com.flashden::MenuItem(). Expected 1, got 0. at flash.display::Sprite/constructChildren() at flash.display::Sprite() at flash.display::MovieClip() at com.flashden::Preview() Below is my menu script: package com.flashden { import flash.display.MovieClip; import flash.text.; import flash.events.MouseEvent; import flash.events.; import flash.net.URLRequest; import flash.display.Loader; public class MenuItem extends MovieClip { private var scope; public var closedX :Number public static const OPEN_MENU = "openMenu"; function callLink(event:MouseEvent):void { public function MenuItem(scope) { // set scope to talk back to -------------------------------// this.scope = scope; // disable all items not to be clickable -------------------// txt_label.mouseEnabled = false; menuItemShine.mouseEnabled = false; menuItemArrow.mouseEnabled = false; // make background clip the item to be clicked (button) ----// menuItemBG.buttonMode = true; // add click event listener to the header background -------// menuItemBG.addEventListener(MouseEvent.CLICK, clickHandler); } private function clickHandler (e:MouseEvent) { scope.openMenuItem(this); } public function loadContent (contentURL:String) { var loader:Loader = new Loader(); configureListeners(loader.contentLoaderInfo); var request:URLRequest = new URLRequest(contentURL); loader.load(request); // place x position of content at the bottom of the header so the top is not cut off ----// loader.x = 35; // we add the content at level 1, because the background clip is at level 0 ----// addChildAt(loader, 0); } private function configureListeners(dispatcher:IEventDispatcher):void { dispatcher.addEventListener(Event.COMPLETE, completeHandler); dispatcher.addEventListener(HTTPStatusEvent.HTTP_STATUS, httpStatusHandler); dispatcher.addEventListener(Event.INIT, initHandler); dispatcher.addEventListener(IOErrorEvent.IO_ERROR, ioErrorHandler); dispatcher.addEventListener(Event.OPEN, openHandler); dispatcher.addEventListener(ProgressEvent.PROGRESS, progressHandler); dispatcher.addEventListener(Event.UNLOAD, unLoadHandler); } private function completeHandler(event:Event):void { //trace("completeHandler: " + event); // remove loader animation ----------------// removeChild(getChildByName("mc_preloader")); } private function httpStatusHandler(event:HTTPStatusEvent):void { // trace("httpStatusHandler: " + event); } private function initHandler(event:Event):void { //trace("initHandler: " + event); } private function ioErrorHandler(event:IOErrorEvent):void { //trace("ioErrorHandler: " + event); } private function openHandler(event:Event):void { //trace("openHandler: " + event); } private function progressHandler(event:ProgressEvent):void { //trace("progressHandler: bytesLoaded=" + event.bytesLoaded + " bytesTotal=" + event.bytesTotal); } private function unLoadHandler(event:Event):void { //trace("unLoadHandler: " + event); } } } Any idea why this is happening?

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  • C++ Templates: implicit conversion, no matching function for call to ctor

    - by noname
    template<class T> class test { public: test() { } test(T& e) { } }; int main() { test<double> d(4.3); return 0; } Compiled using g++ 4.4.1 with the following errors: g++ test.cpp -Wall -o test.exe test.cpp: In function 'int main()': test.cpp:18: error: no matching function for call to 'test<double>::test(double) ' test.cpp:9: note: candidates are: test<T>::test(T&) [with T = double] test.cpp:5: note: test<T>::test() [with T = double] test.cpp:3: note: test<double>::test(const test<double>&) make: *** [test.exe] Error 1 However, this works: double a=1.1; test<double> d(a); Why is this happing? Is it possible that g++ cannot implicitly convert literal expression 1.1 to double? Thanks.

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  • Incorrect new Uri(base, relative) behaviour in .NET

    - by dr. evil
    When you create a new Uri like this: New Uri(New Uri("http://example.com/test.php"),"?x=y") it returns: http://example.com/?x=y It was supposed to return: http://example.com/test.php?x=y according to the every major browser out there (I'm not quite sure what RFC says though). Is this is a bug or is there any other function out there which behaves correctly, also what's the best way to fix it without reinventing the wheel?

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  • Ctor not allowed return type.

    - by atch
    Having code: struct B { int* a; B(int value):a(new int(value)) { } B():a(nullptr){} B(const B&); } B::B(const B& pattern) { } I'm getting err msg: 'Error 1 error C2533: 'B::{ctor}' : constructors not allowed a return type' Any idea why? P.S. I'm using VS 2010RC

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  • How to use a separate class to validate credit card numbers in C#

    - by EvanRyan
    I have set up a class to validate credit card numbers. The credit card type and number are selected on a form in a separate class. I'm trying to figure out how to get the credit card type and number that are selected in the other class (frmPayment) in to my credit card class algorithm: public enum CardType { MasterCard, Visa, AmericanExpress } public sealed class CardValidator { public static string SelectedCardType { get; private set; } public static string CardNumber { get; private set; } private CardValidator(string selectedCardType, string cardNumber) { SelectedCardType = selectedCardType; CardNumber = cardNumber; } public static bool Validate(CardType cardType, string cardNumber) { byte[] number = new byte[16]; int length = 0; for (int i = 0; i < cardNumber.Length; i++) { if (char.IsDigit(cardNumber, i)) { if (length == 16) return false; number[length++] = byte.Parse(cardNumber[i]); //not working. find different way to parse } } switch(cardType) { case CardType.MasterCard: if(length != 16) return false; if(number[0] != 5 || number[1] == 0 || number[1] > 5) return false; break; case CardType.Visa: if(length != 16 & length != 13) return false; if(number[0] != 4) return false; break; case CardType.AmericanExpress: if(length != 15) return false; if(number[0] != 3 || (number[1] != 4 & number[1] != 7)) return false; break; } // Use Luhn Algorithm to validate int sum = 0; for(int i = length - 1; i >= 0; i--) { if(i % 2 == length % 2) { int n = number[i] * 2; sum += (n / 10) + (n % 10); } else sum += number[i]; } return (sum % 10 == 0); } }

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  • Shallow Copy in Java

    - by Vilius
    Hello there! I already know, what a shallow copy is, but I'm not able to impliment it. Here's a short example. public class Shallow { String name; int number; public Shallow (String name, int number) { this.name = name; this.number = number; } } Test the implementation ... public class ShallowTest { public static void main (String[] args) { Shallow shallow = new Shallow("Shallow", 123); Shallow shallowClone = new Shallow(shallow); shallowClone.name = 'Peter'; shallowClone.number = 321; System.out.println(shallow.name + " - " + shallow.number); } } As I purpose, just the reference of the non primitive datatype String would be copied, so that by calling "shallowClone.name = 'Peter';" I would also change the name of "shallow". Am I right? But somehow, it just does not want to work ....

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  • Why Java interfaces can't have constructors?

    - by AndrejaKo
    This question showed up on my mid-term exams and I've been searching for correct answer for some time. I know that Java interfaces can't be directly instantiated so they don't need constructors and that they can have only public static final attributes so they don't need constructors to set them up but that's not the expected answer.

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  • Is it undefined behavior in the case of the private functions call in the initializer list?

    - by Alexey Malistov
    Consider the following code: struct Calc { Calc(const Arg1 & arg1, const Arg2 & arg2, /* */ const ArgN & argn) : arg1(arg1), arg2(arg2), /* */ argn(argn), coef1(get_coef1()), coef2(get_coef2()) { } int Calc1(); int Calc2(); int Calc3(); private: const Arg1 & arg1; const Arg2 & arg2; // ... const ArgN & argn; const int coef1; // I want to use const because const int coef2; // no modification is needed. int get_coef1() const { // calc coef1 using arg1, arg2, ..., argn; // undefined behavior? } int get_coef2() const { // calc coef2 using arg1, arg2, ..., argn and coef1; // undefined behavior? } }; struct Calc is not completely defined when I call get_coef1 and get_coef2 Is this code valid? Can I get UB?

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  • +(void) initialize in objecive c class static variables construstor

    - by sugar
    I found some sample code from here. static UIImage *backgroundImageDepressed; /** * */ @implementation DecimalPointButton + (void) initialize { backgroundImageDepressed = [[UIImage imageNamed:@"decimalKeyDownBackground.png"] retain]; } is it something like this - +(void) initialize method initialize static variables of a class ( interface ) in objective c ? I have never seen this before. Please need your guidance on it. Thanks in advance for sharing your great knowledge. Sagar

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