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In object-oriented programming, there are three related notions of delegation. * In its original usage, delegation refers to one object relying upon another to provide a specified set of functionalities. In research, this is often referred to as consultation or as aggregation in modeling. * In Common Language Infrastructure (CLI), a delegate is a form of type-safe function pointer usually used in an observer pattern as a means of telling which method to call when an event is triggered, keeping the method type.〔 * Rarely, it refers to a programming language feature making use of the method lookup rules for dispatching so-called self-calls as defined by Lieberman in his 1986 paper "Using Prototypical Objects to Implement Shared Behavior in Object-Oriented Systems". Delegation as a language feature supports the prototype-based programming model. Despite delegation being fairly widespread, relatively few major programming languages implement delegation as an alternative model to static inheritance. The Self programming language incorporates the notion of delegation through its notion of mutable parent slots that are used upon method lookup on self calls. In object-oriented programming, a multicast delegate is a delegate that points to several methods.〔(Microsoft Developer Network (MSDN) Article ), ''How to: Combine Delegates (Multicast Delegates)(C# Programming Guide)'', Accessed 5/20/2008〕 Multicast delegation is a mechanism that provides functionality to execute more than one method. There is a list of delegates maintained internally, and when the multicast delegate is invoked, the list of delegates is executed. ==Design pattern== (詳細はaggregation, consultation, or forwarding (when a wrapper object doesn't pass itself to the wrapped object〔(p.20 )〕). Delegation is dependent upon dynamic binding, as it requires that a given method call can invoke different segments of code at runtime. It is used throughout Mac OS X (and its predecessor NeXTStep) as a means of customizing the behavior of program components. It enables implementations such as making use of a single OS-provided class to manage windows, because the class takes a delegate that is program-specific and can override default behavior as needed. 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. It has been argued that delegation may in some cases be preferred to inheritance to make program code more readable and understandable.〔()Trygve Reenskaug, Dept. of Informatics, University of Oslo, "The Case for Readable Code" (2007)〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Delegation (programming)」の詳細全文を読む スポンサード リンク
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