The 'Pico' Personality

What characterizes Pico personality is the fact that for Pico components instantiation and composition phases are collapsed into one, single operation. This is due the fact that Pico components are written with accordance to the type of dependency injection named *Constructor Injection*. Constructor Injection simply means that dependencies are provided (injected) to the component via the constructor.

For Plexus this type of dependency injection is not fundamentally different from other types of dependency injection, which are supported by plexus: Field Dependency Injection, Setter Dependency Injection, Contextualizable Lookup etc. The main differences between Plexus and Pico container is this that our "Pico" friends strongly believe that constructor dependency injection is is superior to anything else and that container can function (almost) without any metadata.

We don't subscribe to this point of view. Plexus' native API promotes Field Dependency Injection and we are recommending using it as it clearly separates two concerns: component instantiation and resolution of component's dependencies. This type of dependency injection makes the encapsulation even stronger as internals of component are not exposed via any public API.

But we leave the choice to users which type of the dependency injection is the most suitable for them. Components are all about composition and composition takes place on meta level of the container and meta data is the glue which makes it possible. We believe that any "serious" container must have rich enough metadata for effectively "plumbing" existing components. We also believe that although we do require much more metadata then Pico, the usage of Plexus is almost as simple as usage of Pico but we provide more powerful options, which are eliminated by the lack of metadata in Pico container. Note also that component testing is often even simpler in case of Plexus then in case of Pico due to the fact that we leverage container as mock infrastructure and we make a use of existing metadata so for example "requirements" (dependencies) of the component does not have to be listed specifically for unit tests. This makes unit tests shorter hence simpler.

Plexus is probably more similar to Nano Container or most likely it is comparable to whatever future Micro Container might be.