Simply Ruby Dependency Injection

di.rb

class Context

  def initialize()
    @cache = {}
  end

  def [](klass)
    if @cache.has_key?(klass)
      @cache[klass]
    else
      inst = klass.instantiateForContext self
      @cache[klass] = inst
      inst.injectWithContext self
      inst
    end
  end

  def new(klass)
    inst = klass.instantiateForContext(self)
    inst.injectWithContext self
    inst
  end

  def []=(key, value)
    @cache[key] = value
  end

end


class Class
  def instantiateForContext(context)
    new
  end
end

class Object
  def injectWithContext(context)
  end
end

example.rb

class Foo
  def injectWithContext(context)
    @bar = context[Bar]
  end
  
  #...
end

class Bar
  # no dependencies
  # ...
end

class Baz
  def injectWithContext(context)
    @foo = context[Foo]
    @bar = context[Bar]
  end
  
  #...
end

ios.rb

class NSNotificationCenter
  def self.instantiateForContext(context)
    defaultCenter
  end
end

class PFInstallation
  def self.instantiateForContext(context)
    PFInstallation.currentInstallation
  end
end