Medicine

Simple Dependency Injection for Ruby

Find yourself passing dependencies in to the initalizer? Medicine makes this declarative.

class CastVote
  include Medicine.di

  dependency :votes_repo, default: -> { Vote }

  def call(entry_id)
    vote_repo.create!(entry_id: entry_id)
  end
end


cast_vote = CastVote.new
cast_vote.call(3)

In this example Medicine adds a private method called vote_repo which returns Vote.

Injecting a dependency

vote_repo = double('VoteRepo')
cast_vote = CastVote.new(vote_repo: vote_repo)

If you want to arguments other than the dependencies in to the constructor don't forget to invoke super:

def initialize(arg1, arg2, dependencies = {})
  @arg1 = arg1
  @arg2 = arg2
  super(dependencies)
end

Required dependencies

dependency :vote_repo

When no default is specified and is not injected an exception will be raised on initialization.

Default dependencies

dependency :vote_repo, default: :vote
dependency :vote_repo, default: :Vote
dependency :vote_repo, default: 'Vote'
dependency :vote_repo, default: -> { Vote }

The above examples will expose a method called vote_repo which returns the Vote class as the default dependency.