Abstract the composition root in a reusable library
c#, composition, dependency-injection, design-patterns
Solution
The description of the Composition Root pattern explicitly states that it can be implemented without a DI Container. The pattern is independent of container usage, and can be used with or without a container.
The Composition Root is the entry point of an application. By definition, it has no callers so it makes no sense to abstract it.
To quote the above article:
The Composition Root is an application infrastructure component.
Only applications should have Composition Roots. Libraries and frameworks shouldn't.
(bold my emphasis)
AutoFixture is a library, and thus has no Composition Root. The `Fixture` class is Façade, in the spirit of building a DI-friendly library.
Problem
In my first question Locate the correct composition root for a .NET library helped clarifying about Dependency Injection. The exhaustive answer of Steven states (in few words if it possible) that a reusable library is a particular a case and here we can use `poor-man-injection` (see the answer for completeness). Studying the source code of AutoFixture, you can note that the main assembly use DI everywhere without depending on a container; something well explained in Mark Seemann book. The question is: can someone introduce a pattern (or good practice) to to abstract the composition root without using a container? Further notes (optional): Backing to AutoFixture where the composition root occurs in `Fixture` type constructors; I think that `*Relays` class are used to group instances in a similar manner some DI library has the concept of module. It's interesting note that there's a type named `BehaviourRoot` that sits on the top of the graph (is this the kind of abstraction I'm searching?).