Add :injector_mixin plugin

[timriley]

The :injector_mixin plugin makes it an easy one-liner to define a constant for the given container's auto-injector mixin.

This way you never have to worry about doing Deps = MyContainer.injector anywhere.

It looks like this:

module MyApp
  class MyContainer < Dry::System::Container
    use :injector_mixin

    configure do |config|
      # ...
    end
  end
end

By this point, there will now be a MyApp::Deps defined, which you can mix into your component classes as usual, e.g. include Deps["some_dependency"].

You can also customise the name:

• use :injector_mixin, name: "Inject" will create MyApp::Inject
• use :injector_mixin, name: "Nested::Inject" will create MyApp::Nested::Inject
• use :injector_mixin, name: "::Inject will create ::Inject

The mixin constant is defined in the container's after-configure hook, since we rely on the inflector for camelizing and constantizing, and we want to give the user an opportunity to provide a custom inflector.

[timriley]

My big question here: what do you think about the name? I'm definitely not wedded to injector_mixin, so I'm open to other suggestions.

Now that I think about it, AFAIK "mixin" is not really an "official" term within Ruby, so perhaps injector_const or injector_constant might be better if we want a self-descriptive name.

[timriley]

Rubocop is saying:

Lint/MissingSuper: Call `super` to initialize state of the parent class.

Do we really think we need to do this here?

[francois]

I have a feeling we should always delegate to super. Who knows where this class can end up being used later? If it doesn't properly delegate, this would break expectations.

[timriley]

My question is more about whether it's really necessary when inheriting from Module. We already don't do it across the other instances of Module inheritance in this codebase, and it's not something that's appeared necessary to me when using this technique elsewhere.

[flash-gordon]

@timriley I doubt it plays a role in this particular case. It's not a problem to have super calls to quell rubocop, though

[solnic]

I think it's beneficial to have a habit of calling super, even if it's a noop. It may happen that you really need to call super, but you don't have this habit and you end up debugging why things don't work just realize you forgot to call super. Been there done that 🙂

[flash-gordon]

can I use different strategies with this? I usually have something like

    Import = injector(dynamic: env.eql?('test')) # default strategy is effects provided by Dry::Effects::System::Container
    KwargsImport = injector(effects: false)      # here opt out back to kwargs

[timriley]

@flash-gordon hmm, no! I've not seen this kind of advanced use case before. Would you have ideas about if/how we could support it?

[flash-gordon]

API-wise I'd expect use :injector_mixin, dynamic: ENV['APP_ENV'].eql?('test') where all extra options are transparently passed to the injector builder (i.e. container.injector).