Interfaces in CoffeeScript

interfaces.coffee

class Host
  constructor: ->
    interfaces = @constructor.interfaces

    if interfaces?
      for interface in interfaces
        _.extend @, interfaces

  @implements: (host, interface) ->
    # This effectively makes host optional
    unless interface?
      interface = host
      host = @
    
    host.interfaces ?= []

    for name, property of interface
      if _.isFunction property
        requisite = property()
      else
        requisite = property
    
      unless name of host
        throw new Error """
          The #{ name } interface requires an implementation
          of #{ name }, but one was not provided for
          #{ host.name }.
        """
  
      implementation = host[name]

      # TODO: Validate requisite.

      host.interfaces.push interface


Events =
  on:
    arguments: ['string', 'function']


# Example leveraging a Base class
class Fruit extends InterfaceHost
  @implements Events
  

# Example without a Base class
class Vehicle
  constructor: -> Host.apply @

# Using arguments:
Host.implements Vehicle, Events

# or by applying context:
Host.implements.apply Vehicle, Events