Thursday, March 06, 2008

NDependency Injection: HasCollection Enforces Layered Architecture

I recently added a feature to NDependencyInjection called "HasCollection".

It lets you specify a set of subsystems that all provide the same interface and so can be viewed as a collection.

ISystemDefinition book = new SystemWiring();

book.HasCollection(Page1, Page2, Page2).Provides();

Here Page1, Page2, Page3 are all of type ISubsystemBuilder, which each define the wiring of a specific IPage.

You can only expose something from one of these subsystems if all subsystems implement it. This has the side-effect of enforcing Liskov's Substitution Principle.

At first this feels limiting, but it is leading us to better designs.

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