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  • Creating instance in java class

    - by aladine
    Please advise me the difference between two ways of declaration of java constructor public class A{ private static A instance = new A(); public static A getInstance() { return instance; } public static void main(String[] args) { A a= A.getInstance(); } } AND public class B{ public B(){}; public static void main(String[] args) { B b= new B(); } } Thanks

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  • Inlining an array of non-default constructible objects in a C++ class

    - by porgarmingduod
    C++ doesn't allow a class containing an array of items that are not default constructible: class Gordian { public: int member; Gordian(int must_have_variable) : member(must_have_variable) {} }; class Knot { Gordian* pointer_array[8]; // Sure, this works. Gordian inlined_array[8]; // Won't compile. Can't be initialized. }; As even beginner C++ users know, the language guarantees that all members are initialized when constructing a class. And it doesn't trust the user to initialize everything in the constructor - one has to provide valid arguments to the constructors of all members before the body of the constructor even starts. Generally, that's a great idea as far as I'm concerned, but I've come across a situation where it would be a lot easier if I could actually have an array of non-default constructible objects. The obvious solution: Have an array of pointers to the objects. This is not optimal in my case, as I am using shared memory. It would force me to do extra allocation from an already contended resource (that is, the shared memory). The entire reason I want to have the array inlined in the object is to reduce the number of allocations. This is a situation where I would be willing to use a hack, even an ugly one, provided it works. One possible hack I am thinking about would be: class Knot { public: struct dummy { char padding[sizeof(Gordian)]; }; dummy inlined_array[8]; Gordian* get(int index) { return reinterpret_cast<Gordian*>(&inlined_array[index]); } Knot() { for (int x = 0; x != 8; x++) { new (get(x)) Gordian(x*x); } } }; Sure, it compiles, but I'm not exactly an experienced C++ programmer. That is, I couldn't possibly trust my hacks less. So, the questions: 1) Does the hack I came up with seem workable? What are the issues? (I'm mainly concerned with C++0x on newer versions of GCC). 2) Is there a better way to inline an array of non-default constructible objects in a class?

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  • call_user_function_array() and __construct

    - by John
    I'm working on a simple framework, and I'm having a slight problem. I'd like to use call_user_function_array() to pass parameters to a function. That's fine, except the function I want to pass it to is __construct. I can't create an instance of an object with cufa(), and by instantiating an object, and then using cufa to call that instance's __construct(), I run into problems with a broken class because I'm calling the constructor twice (and one time it's called wrong.)

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  • CodeContracts: How to fullfill Require in Ctor using this() call?

    - by mafutrct
    I'm playing around with Microsoft's CodeContracts and encountered a problem I was unable to solve. I've got a class with two constructors: public Foo (public float f) { Contracts.Require(f > 0); } public Foo (int i) : this ((float)i) {} The example is simplified. I don't know how to check the second constructor's f for being 0. Is this even possible with Contracts?

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  • C# Strange Behavior

    - by Betamoo
    I have a custom struct : struct A { public int y; } a custom class with empty constuctor: class B { public A a; public B() { } } and here is the main: static void Main(string[] args) { B b = new B(); b.a.y = 5;//No runtime errors! Console.WriteLine(b.a.y); } When I run the above program, it does not give me any errors, although I did not initialize struct A in class B constructor..'a=new A();'

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  • How to define an aspectj pointcut that picks out all constructors of a class that has a specific annotation?

    - by PineForest
    Here is the annotation: @Target(value = ElementType.TYPE) @Retention(value = RetentionPolicy.RUNTIME) @Inherited public @interface MyAnnotation { String name(); } Here is one annotated class: @MyAnnotation(name="foo") public class ClassA { public ClassA() { // Do something } } Here is a second annotated class: @MyAnnotation(name="bar") public class ClassB { public ClassB(String aString) { // Do something } } I am looking for an aspectj pointcut that correctly matches the constructors for ClassA and ClassB while not matching any other constructor for any other class NOT annotated by MyAnnotation.

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  • purpose of php consutructor

    - by Bharanikumar
    Hi , Am working in the classes and object class structure , but not extream level , Just class and function , then in one place instantiation . that's it , not much big functions like __construct etc , Please tell me very simply , 1.what is th purpose of constructor ad destructor , But i know theoretical explanation school level , But i am expecting something like in real time , which situation we have to use, and is there any example for that please tell me, Regards

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  • What's the proper term for a function inverse to a constructor - to unwrap a value from a data type?

    - by Petr Pudlák
    Edit: I'm rephrasing the question a bit. Apparently I caused some confusion because I didn't realize that the term destructor is used in OOP for something quite different - it's a function invoked when an object is being destroyed. In functional programming we (try to) avoid mutable state so there is no such equivalent to it. (I added the proper tag to the question.) Instead, I've seen that the record field for unwrapping a value (especially for single-valued data types such as newtypes) is sometimes called destructor or perhaps deconstructor. For example, let's have (in Haskell): newtype Wrap = Wrap { unwrap :: Int } Here Wrap is the constructor and unwrap is what? The questions are: How do we call unwrap in functional programming? Deconstructor? Destructor? Or by some other term? And to clarify, is this/other terminology applicable to other functional languages, or is it used just in the Haskell? Perhaps also, is there any terminology for this in general, in non-functional languages? I've seen both terms, for example: ... Most often, one supplies smart constructors and destructors for these to ease working with them. ... at Haskell wiki, or ... The general theme here is to fuse constructor - deconstructor pairs like ... at Haskell wikibook (here it's probably meant in a bit more general sense), or newtype DList a = DL { unDL :: [a] -> [a] } The unDL function is our deconstructor, which removes the DL constructor. ... in The Real World Haskell.

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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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  • Dependency Injection Constructor Madness

    - by JP
    I find that my constructors are starting to look like this: public MyClass(Container con, SomeClass1 obj1, SomeClass2, obj2.... ) with ever increasing parameter list. Since "Container" is my dependency injection container, why can't I just do this: public MyClass(Container con) for every class? What are the downsides? If I do this, it feels like I'm using a glorified static. Please share your thoughts on IoC and Dependency Injection madness. Thanks in advance. -JP

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  • XmlSerializer giving FileNotFoundException at constructor

    - by Irwin
    An application I've been working with is failing when i try to serialize types. A statement like this: XmlSerialzer lizer = new XmlSerializer(typeof(MyType)); Produces: System.IO.FileNotFoundException occurred Message="Could not load file or assembly '[Containing Assembly of MyType].XmlSerializers, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null' or one of its dependencies. The system cannot find the file specified." Source="mscorlib" FileName="[Containing Assembly of MyType].XmlSerializers, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null" FusionLog="" StackTrace: at System.Reflection.Assembly._nLoad(AssemblyName fileName, String codeBase, Evidence assemblySecurity, Assembly locationHint, StackCrawlMark& stackMark, Boolean throwOnFileNotFound, Boolean forIntrospection) at System.Reflection.Assembly.nLoad(AssemblyName fileName, String codeBase, Evidence assemblySecurity, Assembly locationHint, StackCrawlMark& stackMark, Boolean throwOnFileNotFound, Boolean forIntrospection) I don't define any special serializers for my class.

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  • Using reflection to retrieve constructor used to instantiate attribute

    - by summatix
    How can I retrieve information about how an attribute was instantiated? Consider I have the following class definitions: [AttributeUsage(AttributeTargets.Class)] public class ExampleAttribute : Attribute { public ExampleAttribute(string value) { Value = value; } public string Value { get; private set; } } [ExampleAttribute("test")] public class Test { } The new .NET 4.0 MemberInfo.GetCustomAttributesData method: foreach (var attribute in typeof(Test).GetCustomAttributesData()) { Console.WriteLine(attribute); } outputs [Example.ExampleAttribute("test")]. Is there another way to retrieve this same information, preferably using the MemberInfo.GetCustomAttributes method?

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  • WPF MVVM ViewModel constructor designmode

    - by Snake
    Right, I've got a main wpf window: <Window x:Class="NorthwindInterface.MainWindow" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" xmlns:ViewModels="clr-namespace:NorthwindInterface.ViewModels" Title="MainWindow" Height="350" Width="525"> <Window.DataContext> <ViewModels:MainViewModel /> </Window.DataContext> <ListView ItemsSource="{Binding Path=Customers}"> </ListView> </Window> And the MainViewModel is this: class MainViewModel : INotifyPropertyChanged { public event PropertyChangedEventHandler PropertyChanged = delegate { }; public MainViewModel() { Console.WriteLine("test"); using (NorthwindEntities northwindEntities = new NorthwindEntities()) { this.Customers = (from c in northwindEntities.Customers select c).ToList(); } } public List<Customer> Customers { get;private set; } Now the problem is that in designermode I can't see my MainViewModel, it highlights it saying that it can't create an instance of the MainViewModel. It is connecting to a database. That is why (when I comment the code the problem is solved). But I don't want that. Any solutions on best practices around this?

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  • Ambiguous function/constructor call in C#

    - by Ahmed Said
    The following code causes a compiler error, as it is ambiguous call but the problem if we use object instead of ArrayList no error happens and the string version works fine; Do you have an explanation for that? class A { public A(string x) { Console.WriteLine("string"); } public A(ArrayList x) { Console.WriteLine("ArrayList"); } } static void Main(string[] args) { A o = new A(null); }

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  • F# Class with Generics : 'constructor deprecated' error

    - by akaphenom
    I am trying to create a a class that will store a time series of data - organized by groups, but I had some compile errors so I stripped down to the basics (just a simple instantiation) and still can't overcome the compile error. I was hoping some one may have seen this issue before. Clas is defined as: type TimeSeriesQueue<'V, 'K when 'K: comparison> = class val private m_daysInCache: int val private m_cache: Map<'K, 'V list ref > ref; val private m_getKey: ('V -> 'K) ; private new(getKey) = { m_cache = ref Map.empty m_daysInCache = 7 ; m_getKey = getKey ; } end So that looks OK to me (it may not be, but doesnt have any errors or warnings) - the instantiation gets the error: type tempRec = { someKey: string ; someVal1: int ; someVal2: int ; } let keyFunc r:tempRec = r.someKey // error occurs on the following line let q = new TimeSeriesQueue<tempRec, string> keyFunc This construct is deprecated: The use of the type syntax 'int C' and 'C ' is not permitted here. Consider adjusting this type to be written in the form 'C' NOTE This may be simple stupidity - I am just getting back from holiday and my brain is still on time zone lag...

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  • Scala Array constructor?

    - by Lukasz Lew
    scala> val a = Array [Double] (10) a: Array[Double] = Array(10.0) scala> val a = new Array [Double] (10) a: Array[Double] = Array(0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0) Why these two expressions have different semantics?

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  • Simple factory to retrieve files using constructor dependency injection

    - by mrblah
    I want to create a class, that is flexible so I can switch implementations. Problem: Store files/documents Options: either store locally on the server filesystem, database or etc. Can someone help with a skeleton structure of the class, and how I would call it? I am not using an IoC, and don't really want to just yet. I just want the flexibility where I would make maybe 1 code change in the factory to call another implementation.

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  • Classes, constructor and pointer class members

    - by pocoa
    I'm a bit confused about the object references. Please check the examples below: class ListHandler { public: ListHandler(vector<int> &list); private: vector<int> list; } ListHandler::ListHandler(vector<int> &list) { this->list = list; } Here I would be wasting memory right? So the right one would be: class ListHandler { public: ListHandler(vector<int>* list); private: vector<int>* list; } ListHandler::ListHandler(vector<int>* list) { this->list = list; } ListHandler::~ListHandler() { delete list; }

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  • troubles with generated constructor in linq2sql

    - by zerkms
    After adding one more table to linq2sql .dbml schema i got Value cannot be null. Parameter name: mapping Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code. Exception Details: System.ArgumentNullException: Value cannot be null. Parameter name: mapping and it refers to autogenerated file: Line 45: #endregion Line 46: Line 47: public db() : Line 48: base(global::data.Properties.Settings.Default.nanocrmConnectionString, mappingSource) Line 49: { Any ideas why this hapenned and how to solve this?

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  • Constructor is being invoked twice

    - by Knowing me knowing you
    In code: LINT a = "12"; LINT b = 3; a = "3";//WHY THIS LINE INVOKES CTOR? std::string t = "1"; //LINT a = t;//Err NO SUITABLE CONV FROM STRING TO LINT. Shouldn't ctor do it? #pragma once #include "LINT_rep.h" class LINT { private: typedef LINT_rep value_type; const value_type* my_data_; template<class T> void init_(const T&); public: LINT(const char* = 0); LINT(const std::string&); LINT(const LINT&); LINT(const long_long&); LINT& operator=(const LINT&); virtual ~LINT(void); LINT operator+()const; //DONE LINT operator+(const LINT&)const;//DONE LINT operator-()const; //DONE LINT operator-(const LINT&)const;//DONE LINT operator*(const LINT&)const;//DONE LINT operator/(const LINT&)const;///WAITS FOR APPROVAL LINT& operator+=(const LINT&);//DONE LINT& operator-=(const LINT&);//DONE LINT& operator*=(const LINT&);//DONE LINT operator/=(const LINT&);///WAITS FOR APPROVAL }; in line number 3 instead of assignment optor ctor is invoked. Why? I'm willing to uppload entire solution on some server otherwise it's hard to put everything in here. I can also upload video file. Another thing is that when I implement this assignment optor I'm getting an error that this optor is already in obj file? What's going on?

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  • Use Lambda in Attribute constructor to get method's parameters

    - by Anthony Shaw
    I'm not even sure if this is possible, but I've exhausted all of my ideas trying to figure this out, so I figured I'd send this out to the community and see what you thought. And, if it's not possible, maybe you'd have some ideas as well. I'm trying to make an Attribute class that I can add to a method that would allow me to use a lambda expression to get each parameter of the method public ExampleAttribute : Attribute { public object Value { get; set; } public ExampleAttribute(--something here to make the lambda work--, object value) { Value = value; } } I'd like to be able to something like this below: [Example(x=x.Id, 4)] [Example(x=x.filter, "string value")] public ActionResult Index(int Id, string filter) { return View(); } I understand that I might be completely dreaming with this idea. I'm basically trying to write a model to allow for self-documenting REST API Documentation. In a recent project here at work we wrote a dozen or so services with 5 to 15 methods on each, I figure it's easier to write something to do this, than to hand code a documentation page for each. I would plan to eventually release this as an open-source project once I have it in a place that I feel it's releasable.

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