Inversion of control (IoC) is an abstract principle describing an aspect of some software architecture designs in which the flow of control of a system is inverted in comparison to procedural programming.

In traditional programming the flow of the business logic is controlled by a central piece of code, which calls reusable subroutines that perform specific functions. Using Inversion of Control this "central control" design principle is abandoned. The caller's code deals with the program's execution order, but the business knowledge is encapsulated by the called subroutines. In practice, Inversion of Control is a style of software construction where reusable generic code controls the execution of problem-specific code. It carries the strong connotation that the reusable code and the problem-specific code are developed independently, which often results in a single integrated application. Inversion of Control as a design guideline serves the following purposes:

  • There is a decoupling of the execution of a certain task from implementation.
  • Every system can focus on what it is designed for.
  • The systems make no assumptions about what other systems do or should do.
  • Replacing systems will have no side effect on other systems.

Dependency injection and Inversion of Control are closely related. The difference between them is discussed in this question.

wikipedia: Inversion of Control

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