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There is a list of delegates maintained internally, and when the multicast delegate is invoked, the list of delegates is executed. In C#, delegates are often used to implement callbacks in event driven programming. For example, a delegate may be used to indicate which method should be called when the user clicks on some button.
An event requires an accompanied event handler that is made from a special delegate that in a platform specific library like in Windows Presentation Foundation and Windows Forms usually takes two parameters: sender and the event arguments. The type of the event argument-object derive from the EventArgs class that is a part of the CLI base library.
For instance, when the user clicks the close box, the window manager sends the delegate a windowShouldClose: call, and the delegate can delay the closing of the window, if there is unsaved data represented by the window's contents. Delegation can be characterized (and distinguished from forwarding) as late binding of self: [4]
In the delegate pattern, this is instead accomplished by explicitly passing the original object to the delegate, as an argument to a method. [1] " Delegation" is often used loosely to refer to the distinct concept of forwarding , where the sending object simply uses the corresponding member on the receiving object, evaluated in the context of ...
Delegate (CLI), a form of type-safe function pointer used by the Common Language Infrastructure (CLI), specifying both a method to call and optionally an object to call the method on. See also [ edit ]
CLI languages such as C# and VB.NET provide a type-safe encapsulating function reference known as delegate. Events and event handlers, as used in .NET languages, provide for callbacks. Functional languages generally support first-class functions, which can be passed as callbacks to other functions, stored as data or returned from functions.
Like the Qt framework's pseudo-C++ signal and slot, C# has semantics specifically surrounding publish-subscribe style events, though C# uses delegates to do so. C# offers Java-like synchronized method calls, via the attribute [MethodImpl(MethodImplOptions.Synchronized)], and has support for mutually-exclusive locks via the keyword lock.
Functors used in this manner are analogous to the original mathematical meaning of functor in category theory, or to the use of generic programming in C++, Java or Ada. In Haskell, the term functor is also used for a concept related to the meaning of functor in category theory. In Prolog and related languages, functor is a synonym for function ...