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)

# or

cast_vote = CastVote.new(arg1, arg2, vote_repo: vote_repo)

Required dependencies

dependency :vote_repo

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

Default dependencies

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.

You could also pass an object which responds to call and accepts one argument, the name of the dependency

dependency :vote_repo, default: Repo

class Repo
  def self.call(name)
    Kernel.constant_get(name.gsub('_repo', ''))
  end
end

In this example the vote_repo method will return the Vote class.