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  • C# - Why can't I enforce derived classes to have parameterless constructors?

    - by FrisbeeBen
    I am trying to do the following: public class foo<T> where T : bar, new { _t = new T(); private T _t; } public abstract class bar { public abstract void someMethod(); // Some implementation } public class baz : bar { public overide someMethod(){//Implementation} } And I am attempting to use it as follows: foo<baz> fooObject = new foo<baz>(); And I get an error explaining that 'T' must be a non-abstract type with a public parameterless constructor in order to use it as parameter 'T' in the generic type or method. I fully understand why this must be, and also understand that I could pass a pre-initialized object of type 'T' in as a constructor argument to avoid having to 'new' it, but is there any way around this? any way to enforce classes that derive from 'bar' to supply parameterless constructors?

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  • Calling some functions before main in C

    - by minjang
    I'd like to do some stuffs before main function. I have multiple source files. In each file, there is some work that needs to be done before main. It was no problem in C++, but problematic with C. In C++, this can be done by two ways: Exploiting a constructor of a global class/struct. Calling a function to a global variable For example, static const int __register_dummy_ = __AddRegisterMetaInfo(...); However, in C, either ways is impossible. Obviously, there is no constructor. So, the first option is inherently impossible. I thought that the second option would be possible, but not compiled in C (I tested only with Visual C++. It gives C2099.). C only allows a constant to a non-automatic variable. Is there any way to call some functions before main?

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  • How can a class's memory-allocated address be determined from within the contructor?

    - by Jim Fell
    Is it possible to get the memory-allocated address of a newly instantiated class from within that class's constructor during execution of said constructor? I am developing a linked list wherein multiple classes have multiple pointers to like classes. Each time a new class instantiates, it needs to check its parent's list to make sure it is included. If I try to do something like this: MyClass() // contructor { extern MyClass * pParent; for ( int i = 0; i < max; i++ ) { pParent->rels[i] == &MyClass; // error } } I get this error: error C2275: 'namespace::MyClass' : illegal use of this type as an expression Any thoughts or suggestions would be appreciated. Thanks.

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  • Is there a way to cause a new C++ class instance to fail, if certain conditions in the contructor ar

    - by Jim Fell
    As I understand it, when a new class is instantiated in C++, a pointer to the new class is returned, or NULL, if there is insufficient memory. I am writing a class that initializes a linked list in the constructor. If there is an error while initializing the list, I would like the class instantiator to return NULL. For example: MyClass * pRags = new MyClass; If the linked list in the MyClass constructor fails to initialize properly, I would like pRags to equal NULL. I know that I can use flags and additional checks to do this, but I would like to avoid that, if possible. Does anyone know of a way to do this? Thanks.

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  • How should i be handling string Interning on deserialization?

    - by DayOne
    In the example below I am interning the string in the constructor which is fine. However when i deserialise the object from the binary formatter I don't think the string will be interned as the constructor should be called. How should I be ensuring the _name string is interned? ... or will it be interned ok? Thanks [Serializable] class City { private readonly string _name; public City(string t) { _name = string.Intern(t); } public string Name { get { return _name; } } public override string ToString() { return _name; } }

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  • How to find the entity with the greatest primary key?

    - by simpatico
    I've an entity LearningUnit that has an int primary key. Actually, it has nothing more. Entity Concept has the following relationship with it: @ManyToOne @Size(min=1,max=7) private LearningUnit learningUnit; In a constructor of Concept I need to retrieve the LearningUnit with the greatest primary key. If no LearningUnit exists yet I instantiate one. I then set this.learningUnit to the retrieved/instantied. Finally, I call the empty constructor of Concept in a try-catch block, to have the entitymanager do the cardinality check. If an exception is thrown (I expect one in the case that already another 7 Concepts are referring to the same LearningUnit. In that case, I case instantiate a new LearningUnit with a new greater primary key. Please, also point out, if any, clear pitfalls in my outlined algorithm above.

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  • Is it possible to start an activity from a regular java class?

    - by Yotam
    In my ActionBarSherlock I have the same menu items for all activities, so it seems unwise to define onClick handlers in each activity - they all do the same. Instead I created a class called MyClickListener that implements com.actionbarsherlock.view.MenuItem.OnMenuItemClickListener, and in there I have a simple switch block that starts the appropriate activity. Problem is that Intent constructor's first argument is of type Context, and even when I pass this to MyClickListener's constructor, I can't start any activity. The same goes for every method that has a Context object as a parameter. Is there a way to work around it? What is a context object? Thanks

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  • What is the accepted way to replace java.util.Date(year,month,day)

    - by dagw
    I'm trying to do something really simple, but starting to realize that dates in Java are a bit of minefield. All I want is to get passed groups of three ints ( a year, a month and a date) create some Date objects, do some simple test on them (along the lines of as date A before date B and after January 1 1990), convert them to java.sql.Date objects and pass them off to the database via JDBC. All very simple and works fine using the java.util.Date(int year,int month,int day) constructor. Of course that constructor is depreciated, and I'd like to avoid using depreciated calls in new code I'm writing. However all the other options to solve this simple problem seem stupidly complicated. Is there really no simple way to do what I want without using depreciated constructors? I know the standard answer to all Java date related questions is "use joda time", but I really don't want to start pulling in third party libraries for such a seemingly trivial problem.

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  • How to make c# don't call destructor of a instance

    - by Bình Nguyên
    I have two forms and form1 needs to get data from form2, i use a parameter in form2 constructor to gets form1's instance like this: public form2(Form form1) { this.f = form1; } and in form1: Form form2 = new Form(this); But it seem form1 destruct was called when i closed form1. my question is how can i avoid this problem? EDIT: I have many typing mistakes in my question, i'm so sorry, fixed: I have two forms and form2 needs to get data from form1, i use a parameter in form1 constructor to gets form1's instance like this: private Form f; public form2(Form form1) { this.f = form1; } and in form1: Form form2 = new Form(this); But it seem form1 destruct was called when i closed form2. my question is how can i avoid this problem?

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  • Selecting size of vector of vectors

    - by xbonez
    I have a class called Grid that declares a vector of vectors like this: typedef vector<int> row; typedef vector<row> myMatrix; myMatrix sudoku_; The constructor looks like this: grid::grid() : sudoku_(9,9) { } As you can see, the constructor is initializing it to be a 9x9 grid. How can I make it work so that the user is asked for a number, say n, and the grid is initialized n x n ?

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  • What did I do wrong here when trying to unit test a class that references a web service

    - by zachary
    So I had a class that referenced a class that referenced another class that called a web service. So I learn how to create an interface using partial classes. I inject the web service through the constructor. Then my unit test fails because I am newing up the actual web service in the second level of the class. So I end up modifying all three classes to pass the web service down through the constructor... was not happy :-( gave up.... what should I be doing in this case?

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  • Problems using Custom Layout in XML

    - by Kevin
    I've created a new GridLayout class that I want to use in an XML File. The class is in another project. I've created the attrs.xml file in the other project with my properties but when the constructor gets called with the AttributeSet, none of the values are set. In my xml for my screen layout, I refer to the layout with the following: xmlns:gridLayout="@com.mastertechsoftware.AndroidUtil:http://schemas.android.com/apk/res/com.mastertechsoftware.AndroidUtil" Not sure if that is right. I have the attrs.xml file being compiled to R.java in com/mastertechsoftware/AndroidUtil. All the right styleable values are there. In my constructor, I use: TypedArray a = c .obtainStyledAttributes(attrs, R.styleable.GridLayout); this.numRows = a.getInt(R.styleable.GridLayout_numRows, -1); Nothing comes back (-1 does but that means nothing is there) If I use int n = a.getIndexCount(); I get 0.

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  • How to persist every new entity?

    - by simpatico
    I expect every instantiated entity to correspond to a tuple (& co) in the database. In the examples I see around, one always instantiates the entity (via a constructor) and then calls persist with that entity. I find this error-prone, and was wondering if it wasn't possible to have every instantiated entity automatically managed/persisted/reflected to the database (at least intended to). This also seems to prevent me from persisting instance variable entities. I.e. I've an entity which instantiates another (entities it has an association with) in its constructor.

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  • Returning and instance of a Class given its .class (MyClass.class)

    - by jax
    I have an enum that will hold my algorithms. I cannot instantiate these classes because I need the application context which is only available once the application has started. I want to load the class at runtime when I choose by calling getAlgorithm(Context cnx). How do I easily instantiate a class at runtime given its .class (and my constructor takes arguments)? All my classes are subclasses of Algorithm. public enum AlgorithmTypes { ALL_FROM_9_AND_LAST_FROM_10_ID(AlgorithmFactory.AlgorithmAllFrom9AndLastFrom10Impl.class), ALL_FROM_9_AND_LAST_FROM_10_CURRENCY_ID(AlgorithmFactory.AlgorithmAllFrom9AndLastFrom10Impl.class), DIVIDE_BY_9_LESS_THAN_100(AlgorithmFactory.AlgorithmAllFrom9AndLastFrom10Impl.class), TABLES_BEYOND_5_BY_5(AlgorithmFactory.AlgorithmAllFrom9AndLastFrom10Impl.class); private Class<? extends Algorithm> algorithm; AlgorithmTypes(Class<? extends Algorithm> c) { algorithm = c; } public Algorithm getAlgorithm(Context cnx) { return //needs to return the current algoriths constructor which takes the Context Algorithm(Context cnx); } }

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  • Confusion over C++ new operator and classes

    - by Nils
    Hi all I created a simple class in C++ which has a private dynamic array. In the constructor I initialize the array using new and in the destructor I free it using delete. When I instantiate the class using Class a = Class(..); it works as expected, however it seems I cannot instantiate it using the new operator (Like Class *a = new Class(..);), I always get a segmentation fault. What I don't understand is when I should use new to instantiate a class and when just call the constructor or should it be possible to instantiate a class either with new or by just calling the constructor. float** A = new float*[3]; for (int i=0; i<3; i++) { A[i] = new float[3]; } A[0][0] = 3; A[0][1] = 3; A[0][2] = 4; A[1][0] = 5; A[1][1] = 6; A[1][2] = 7; A[2][0] = 1; A[2][1] = 2; A[2][2] = 3; Matrix *M = new Matrix(A, 3, 3); delete[] A; delete M; Below the class definition.. class Matrix { private: int width; int height; int stride; float* elements; public: Matrix(float** a, int n, int m); ~Matrix(); }; Matrix::Matrix(float** a, int n, int m) { // n: num rows // m: elem per rows elements = new float[n*m]; for (int i=0; i<n; i++) { for (int j=0; j<m; j++) { elements[i*n + j] = a[n][m]; } } } Matrix::~Matrix() { delete[] elements; }

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  • Using Boost statechart, how can I transition to a state unconditionally?

    - by nickb
    I have a state A that I would like to transition to its next state B unconditionally, once the constructor of A has completed. Is this possible? I tried posting an event from the constructor, which does not work, even though it compiles. Thanks. Edit: Here is what I've tried so far: struct A : sc::simple_state< A, Active > { public: typedef sc::custom_reaction< EventDoneA > reactions; A() { std::cout << "Inside of A()" << std::endl; post_event( EventDoneA() ); } sc::result react( const EventDoneA & ) { return transit< B >(); } }; This yields the following runtime assertion failure: Assertion failed: get_pointer( pContext_ ) != 0, file /includ e/boost/statechart/simple_state.hpp, line 459

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  • Creating immutable objects from javabean

    - by redzedi
    Hi All, I am involved in this project where we are building on good bit of legacy code. I have a particular situation about one big java bean object which has to be transferred over wire. So my first thought was to make it immutable and serializable to do the trick .At this point I am faced with a few difficult choices :- 1 Ideally I want some way to automatically generate an immutable, serializable version of this class. I dont have the scope to refactor or alter this class in any way and i would really really hate to have to copy paste the class with a different name ?? 2 Assuming that i gave up on 1 i.e i actually chose to duplicate code of the HUGE javabean class , i still will be in the unsavoury situation of having to write a constructor with some 20-25 parameters to make this class immutable. what is a better way to make a class immutable other than constructor injection ?? Thanks and Regards,

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  • How to avoid double construction of proxy with DynamicProxy::CreateClassProxyWithTarget?

    - by Belvasis
    I am decorating an existing object using the CreateClassProxyWithTarget method. However, the constructor and therefore, initialization code, is being called twice. I already have a "constructed" instance (the target). I understand why this happens, but is there a way to avoid it, other than using an empty constructor? Edit: Here is some code: First the proxy creation: public static T Create<T>(T i_pEntity) where T : class { object pResult = m_pGenerator.CreateClassProxyWithTarget(typeof(T), new[] { typeof(IEditableObject), typeof(INotifyPropertyChanged) , typeof(IMarkerInterface), typeof(IDataErrorInfo) }, i_pEntity, ProxyGenerationOptions.Default, new BindingEntityInterceptor<T>(i_pEntity)); return (T)pResult; } I use this for example with an object of the following class: public class KatalogBase : AuditableBaseEntity { public KatalogBase() { Values = new HashedSet<Values>(); Attributes = new HashedSet<Attributes>(); } ... } If i now call BindingFactory.Create(someKatalogBaseObject); the Values and Attributes properties are beeing initialized again.

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  • Fast check if an object will be successfully instantiated in PHP?

    - by Gremo
    How can I check if an object will be successfully instantiated with the given argument, without actually creating the instance? Actually I'm only checking (didn't tested this code, but should work fine...) the number of required parameters, ignoring types: // Filter definition and arguments as per configuration $filter = $container->getDefinition($serviceId); $args = $activeFilters[$filterName]; // Check number of required arguments vs arguments in config $constructor = $reflector->getConstructor(); $numRequired = $constructor->getNumberOfRequiredParameters(); $numSpecified = is_array($args) ? count($args) : 1; if($numRequired < $numSpecified) { throw new InvalidFilterDefinitionException( $serviceId, $numRequired, $numSpecified ); }

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  • i need help to designe code in c++

    - by user344987
    ) Design and implement a Graph data structure. Use adjacency matrix to implement the unweighted graph edges. The Graph must support the following operations: 1.Constructor 2.Destructor 3.Copy constructor 4.A function to add an edge between two nodes in the graph 5.A display function that outputs all the edges of the graph 6.A function edge that accepts two nodes, the function returns true if there is an edge between the passed nodes, and returns false otherwise. B.(100 points) Depth first search and Breadth first search functions. C.(100 points) A function to output a spanning tree of the graph, use any algorithm you find appropriate, also, make the necessary changes on the data structure in A to implement your algorithm.

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  • Constructors + Dependency Injection

    - by Sunny
    If I am writing up a class with more than 1 constructor parameter like: class A{ public A(Dependency1 d1, Dependency2 d2, ...){} } I usually create a "argument holder"-type of class like: class AArgs{ public Dependency1 d1 { get; private set; } public Dependency2 d2 { get; private set; } ... } and then: class A{ public A(AArgs args){} } Typically, using a DI-container I can configure the constructor for dependencies & resolve them & so there is minimum impact when the constructors need to change. Is this considered an anti-pattern and/or any arguments against doing this?

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  • Where to register for C# events?

    - by themaninthesuitcase
    I am currently transitioning from VB to C# and am having some issues with regards to registering my interest in an event. When using VB it was simply a case of specifying that a method Handles and event, often this was generated by using the object events list. While I can easily use the Class.event += delegate in C# I am unsure where the best place is to place the code to do this. Am I best placing it inside of the InitializeComponent() as per the generated code (say if you select the event in the from designer) or should I place it inside the constructor for better readability/maintenance. If inside the constructor, should it be before or after the call to InitializeComponent()?

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  • Why can't I enforce derived classes to have parameterless constructors?

    - by FrisbeeBen
    I am trying to do the following: public class foo<T> where T : bar, new() { public foo() { _t = new T(); } private T _t; } public abstract class bar { public abstract void someMethod(); // Some implementation } public class baz : bar { public overide someMethod(){//Implementation} } And I am attempting to use it as follows: foo<baz> fooObject = new foo<baz>(); And I get an error explaining that 'T' must be a non-abstract type with a public parameterless constructor in order to use it as parameter 'T' in the generic type or method. I fully understand why this must be, and also understand that I could pass a pre-initialized object of type 'T' in as a constructor argument to avoid having to 'new' it, but is there any way around this? any way to enforce classes that derive from 'bar' to supply parameterless constructors?

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  • how to create a dynamic class at runtime in Java

    - by Mrityunjay
    hi, is it possible to create a new java file from existing java file after changing some of its attributes at runtime?? Suppose i have a java file pubic class Student{ private int rollNo; private String name; // getters and setters // constructor } is it possible to create something like this, provided that rollNo is key element for the table.. public class Student { private StudentKey key; private String name; //getters and setters //constructor } public class StudentKey { private int rollNo; // getters and setters // construcotors } please help..

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  • How to access the service instance from host object in WCF?

    - by user1048677
    I am trying to incarnate some sort of ad hoc WCF service. I already managed to launch it and make it call its own web methods as some other guy's methods. The issue that I am facing is instance management. I have set [ServiceBehavior(InstanceContextMode = InstanceContextMode.Single)] so it now has a global instance with the same properties for all clients. But besides that I need it to call other services of its kind while listening to incoming requests from clients (similar crazy services). While debugging I noticed that the ServiceHost's constructor calls the constructor of the service class. So, I assumed it has access to the global instance of this class and I need to find a way to call methods of this instance. Please don't ask what I have been smoking, I just have to make it ad hoc.

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