Sequential Programming - Dependency Injection (DI)

[mpostol]

I want to open a discussion on the following description. Any feedback is welcome.

It is a programming pattern where the abstraction paradigm defined as a part of the object-oriented programming concept is applied to provide an instance of a concrete type when the type is not visible or shall be not referred to for some reason. In other words, the new operator is not applicable to create an instance in a location where this instance is to be used. The lack of possibility to deal directly with the concrete type in concern or deliberate avoiding direct access to this type for some reasons shall be recognized as a problem to be solved.

Below there are selected reasons why a concrete type is not visible or shall not be referred to in a program location:

1. the type in concern is defined in the programming layer above and shall not be used directly to comply with separation of concerns and responsibility rules
2. the type in concern is defined in the not referenced project, for example in the unit test project to provide testing data that must be not located inside of a shippable deliverable and as the result, the type is not visible
3. the type in concern will be defined later for some reason, for example, to avoid waiting for the final implementation when work is forked to be conducted simultaneously by independent developers
4. the type in concern is defined out of the current solution, for example, it is a part of a plug-in