malakai97

Modules in Ruby

On Composition

There has been sentiment that ruby's modules enable composition, but this is not the case. Composition describes a "has-a" relationship, whereas (in ruby) when a class includes a module, it creates an is-a relationship.

Forms/Patterns

There are four basic forms of modules in ruby, some good, some not so good.

malakai97

Superclass.for(obj) # => The concrete subclass instance you wanted

malakai97

Dependency Injection in Ruby 07 Oct 04

Introduction

At the 2004 Ruby Conference, Jamis Buck had the unenviable task to explain Dependency Injection to a bunch of Ruby developers. First of all, Dependency Injection (DI) and Inversion of Control (IoC) is hard to explain, the benefits are subtle and the dynamic nature of Ruby make those benefits even more marginal. Furthermore examples using DI/IoC are either too simple (and don’t convey the usefulness) or too complex (and difficult to explain in the space of an article or presentation). I once attempted to explain DI/IoC to a room of Java programmers (see onestepback.org/articles/dependencyinjection/), so I can’t pass up trying to explain it to Ruby developers.

Thanks goes to Jamis Buck (the author of the Copland DI/IoC framework) who took the time to review this article and provide feedback.

What is Dependency Injection?

malakai97

# lib/mygem/cli.rb

require "mygem"
require "mygem/configuration"
module MyGem
  class CLI

    def actual_cli_method(x,y)
      MyGem.config = configuration(opts)
      MyGem::StuffDoer.new(x).go(y)

malakai97

require 'psych'

class WorseScanner < Psych::ScalarScanner
  def parse_time(s)
    s
  end
end

s = "---\nf: 2001-02-29T01:02:03-03:00" # Note this day doesn't exist.