What Is Inversion of Control? Frameworks, Callbacks, Dependency Injection and Containers

Tue, 20 Oct 2026 23:00:00 +0000

A web framework calls a function when a request arrives. A test runner finds the tests in a file and runs each one. A browser calls a handler when a button is clicked, and an application server hands a class the database connection it asked for in its constructor. In each case the code a programmer wrote does not decide when it runs or where its collaborators come from: something else does. That reversal has a name, inversion of control, and it is one of the ideas most of modern software is quietly built on. This article explains what it means, where the term came from, the forms it takes, how dependency injection and IoC containers work inside, and when the indirection is worth paying for. It closes a series on SOLID: where the dependency inversion principle says which way dependencies should point, this is the mechanism that makes them point that way at run time. Every output shown here was produced by running the code on Windows 11, with Python 3.14.6 and with the .NET 10 SDK and Microsoft.Extensions.DependencyInjection 10.0.13, not written by hand.

Dependency Injection on Artur Rios Lab

What Is Inversion of Control? Frameworks, Callbacks, Dependency Injection and Containers