Manual Dependency Injection
Manual Dependency Injection is a software design pattern where dependencies (objects or services that a class needs) are explicitly provided to a class by an external entity, such as a factory or constructor, rather than being instantiated internally. This promotes loose coupling, enhances testability by allowing easy substitution of dependencies with mocks or stubs, and improves code maintainability by centralizing dependency management. It is a fundamental technique in object-oriented programming for implementing Inversion of Control (IoC).
Developers should use Manual Dependency Injection when building applications that require high testability, such as unit testing with mock dependencies, or when aiming for modular and decoupled code in frameworks that don't include built-in DI containers. It is particularly useful in small to medium-sized projects where the overhead of a full DI framework is unnecessary, or in scenarios where fine-grained control over dependency lifecycle and configuration is needed, such as in legacy systems or performance-critical applications.