[Proof of concept] Component isolation

[cllns]

dry-system provides a nice container for creating new instances of classes, but it doesn't enforce its use. Developers are free to create an object by calling its constant constructor (e.g. Foo.new)

...until now... 😱

With this proposed 'isolation' feature, a component's constant would be removed right after it's loaded, so the users would not be able to call Foo.new. Or call Foo at all. That is, they would have to use the container to create new instances.

This may be a very bad idea... it may be going too far. It may have negative unintended consequences. I could see it being useful in some circumstances though. The idea is to remove more global state, by having fewer constants.

This is clearly just a proof of concept. It could be a post-1.0 feature, too. If we wanted to implement this for real, some things (among more, I'm sure) we'd have to consider:

• How would this be configured? Per component, per component_dir, per container?
• Should this be a custom Loader? i.e. provided as a subclass of Loader, either in this gem or as an external one
• Is this the right place to do this?
• Is isolate/isolation the right name?
• Do we want to go further, and load the class definitions once and store them internally somehow, and remove the constants then, once?

[cllns]

This can also be implemented as a custom Rubocop rule:

module RuboCop
  module Cop
    module Experimental
      class ProhibitClassNew < Base
        MSG = 'Use your dependency injection framework instead of manually creating objects from class constants.'

        RESTRICT_ON_SEND = %i[new].freeze

        def_node_matcher :class_new?, <<~PATTERN
          (send const :new ...)
        PATTERN

        def on_send(node)
          add_offense(node) if class_new?(node)
        end
        alias on_csend on_send
      end
    end
  end
end