Medicine

Simple Dependency Injection for Ruby

Find yourself injecting dependencies via the initalizer or a setter method?

Medicine makes this declarative.

Include the Medicine module and declare the dependencies with dependency.

class CastVote
  include Medicine.di

  dependency :votes_repo, default: -> { Vote }

  def call
    votes_repo # => Vote
  end
end

For each dependency declared a private method is defined which returns the dependency.

command = CastVote.new

In the above case the votes_repo method will return Vote.

If no dependency is injected the default will be used.

Specifying a default is optional and if a dependency is not injected and there is no default an error will be raised if the dependencies method is invoked.

command = CastVote.new(votes_repo: double)

In the above case votes_repo will return the double.

If you try and inject a dependency which has not been declared an error is raised.

command = CastVote.new
command.inject_depdendency(:vote_repo, double)

In the above case votes_repo will return the double.

If you try and inject a dependency which has not been declared an error is raised.

dependency :vote_repo

When no default is specified the dependency must be injected via the constructor or setter an otherwise an exception will be raised.

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

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

If you want to pass 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

Tested with MRI 2.1+ and Rubinius.

See the build status for details.

rspec spec