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In software engineering, inversion of control (IoC) describes a design in which custom-written portions of a computer program receive the flow of control from a generic, reusable library. A software architecture with this design inverts control as compared to traditional procedural programming: in traditional programming, the custom code that expresses the purpose of the program calls into reusable libraries to take care of generic tasks, but with inversion of control, it is the reusable code that calls into the custom, or task-specific, code. Inversion of control is used to increase modularity of the program and make it extensible, and has applications in object-oriented programming and other programming paradigms. The term was popularized by Robert C. Martin and Martin Fowler. The term is related to but different from the dependency inversion principle, which concerns itself with decoupling dependencies between high-level and low-level layers through shared abstractions. == Overview == As an example, with traditional programming, the main function of an application might make function calls into a menu library to display a list of available commands and query the user to select one.〔 The library thus would return the chosen option as the value of the function call, and the main function uses this value to execute the associated command. This style was common in text based interfaces. For example, an email client may show a screen with commands to load new mails, answer the current mail, start a new mail, etc., and the program execution would block until the user presses a key to select a command. With inversion of control, on the other hand, the program would be written using a software framework that knows common behavioral and graphical elements, such as windowing systems, menus, controlling the mouse, and so on. The custom code "fills in the blanks" for the framework, such as supplying a table of menu items and registering a code subroutine for each item, but it is the framework that monitors the user's actions and invokes the subroutine when a menu item is selected. In the mail client example, the framework could follow both the keyboard and mouse inputs and call the command invoked by the user by either means, and at the same time monitor the network interface to find out if new messages arrive and refresh the screen when some network activity is detected. The same framework could be used as the skeleton for a spreadsheet program or a text editor. Conversely, the framework knows nothing about Web browsers, spreadsheets or text editors; implementing their functionality takes custom code. Inversion of control carries the strong connotation that the reusable code and the problem-specific code are developed independently even though they operate together in an application. Software frameworks, callbacks, schedulers, event loops and dependency injection are examples of design patterns that follow the inversion of control principle, although the term is most commonly used in the context of object-oriented programming. Inversion of control serves the following design purposes: * To decouple the execution of a task from implementation. * To focus a module on the task it is designed for. * To free modules from assumptions about how other systems do what they do and instead rely on contracts. * To prevent side effects when replacing a module. Inversion of control is sometimes facetiously referred to as the "Hollywood Principle: Don't call us, we'll call you". 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「Inversion of control」の詳細全文を読む スポンサード リンク
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