medicine

Medicine

Simple Dependency Injection for Ruby

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

Medicine makes this declarative.

Usage

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.

Without injection

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.

Injecting via initializer

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.

Injecting via a setter

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.

Required dependencies

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.

Default dependencies

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.

Already got an initializer?

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

Compatibility

Tested with MRI 2.1+ and Rubinius.

See the build status for details.

Running Specs

rspec spec