Inversion of control

In software engineering, inversion of control (IoC) is a design principle in which custom-written portions of a computer program receive the flow of control from a generic framework. 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 framework 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. The general concept is also related to event-driven programming in that it is often implemented using IoC, so that the custom code is commonly only concerned with handling of events, whereas the event loop and dispatch of events/messages is handled by the framework or the runtime environment.

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