Injectr

Super simple IOC for Rails. This was part of my research for my talk on Exploring IoC in Ruby. Checkout the slides here: https://speakerdeck.com/andypike/exploring-ioc-in-ruby

Warning

This is just an experiment. Injectr has not been properly tested and is not considered production ready.

How to install

Add this to your gem file and run $ bundle:

gem 'injectr', github: 'andypike/injectr'

How to use

Add a new file into your initilizers folder called 'injectr.rb' and specify your components:

Injectr.create_container do |c|
  c.register :craftsman, Carpenter
  c.register :tool, PowerSaw  
  c.register :fixings, Nails  
  c.register :power_source, Electricity
end

If you want to create an instance of one of there classes then just resolve the root:

craftsman = Injectr.resolve(:craftsman)

Injecting into a Rails controller:

Just add an constructor with param names that match the registered keys. No need to register the controllers. DON'T FORGET TO CALL SUPER()

class HomeController < ApplicationController
  def initialize(craftsman)
    super()

    @craftsman = craftsman
  end

  def index
    render :text => @craftsman.build_something
  end
end

What do you need to add to your classes?

Nothing. Just Plain Old Ruby Objects work fine. You only need to match the constructor arg names with the registered keys. Here's an example set that work with the above examples:

class Nails
  def to_s
    "nails"
  end
end
 
class Glue
  def to_s
    "glue"
  end
end
 
class PowerSaw
  def initialize(power_source)
    @power_source = power_source
  end
 
  def to_s
    "#{@power_source} power saw"
  end
end
 
class HandSaw
  def to_s
    "hand saw"
  end
end
 
class Electricity
  def to_s
    "electrical"
  end
end
 
class Carpenter
  def initialize(tool, fixings)
    @tool = tool
    @fixings = fixings
  end
 
  def build_something
    "Building something in wood with #{@fixings} and #{@tool}"
  end
end

Here's a sample Rails app that uses the above if you are interested: https://github.com/andypike/injectr_app

Still To Do

• Handle missing registrations
• Circular dependency detection
• Optional params
• Lifecycle options