Dependency injection (DI) is a design pattern meant to transform hard-coded dependencies into swappable ones, generally at run-time. DI is the primary mechanism by which to implement Inversion of Control (IoC) techniques to load dependencies at run-time as well as the most effortless way to swap dependency implementations with mocks or stubs for unit testing. DI is a best practice that yields more readable and maintainable code due to the way all of an implementation’s dependencies are knowable at-a-glance and by the amazing side effect of creating easily testable code.
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