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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?

baweaver

# sudo gem install bson
# sudo gem install bson_ext
# sudo gem install yajl-ruby
# sudo gem install json
# sudo gem install msgpack

require 'rubygems'
require 'benchmark'
require 'yaml'
require 'bson'

baweaver

divisible_by = -> n, v { v % n == 0 }.curry

(1..100).each { |v|
  puts case v
  when divisible_by[15] then 'FizzBuzz'
  when divisible_by[3]  then 'Fizz'
  when divisible_by[5]  then 'Buzz'
  else
    v
  end

baweaver

grouped_join = -> join:, group_join:, group_count: 3 {
  -> list {
    list.each_slice(group_count).map { _1.join(join) }.join(group_join)
  }
}

# 9x9 Game Board Grid
grid = [[*0..8]] * 9

cell_seperator      = ' '

baweaver

Introduction

Enumerable. Debatably one of, if not the, most powerful features in Ruby. As a majority of your time in programming is dealing with collections of items it's no surprise how frequently you'll see it used.

Difficulty

Foundational

Some knowledge required of functions in Ruby. This post focuses on foundational and fundamental knowledge for Ruby programmers.

baweaver

Introduction

Enumerable. Debatably one of, if not the, most powerful features in Ruby. As a majority of your time in programming is dealing with collections of items it's no surprise how frequently you'll see it used.

Difficulty

Foundational

Some knowledge required of functions in Ruby. This post focuses on foundational and fundamental knowledge for Ruby programmers.

baweaver

def roman_numeral(n) = case n
  in 1000..3000 then 'M'  + roman_numeral(n - 1000)
  in 900..999   then 'CM' + roman_numeral(n - 900)
  in 500..899   then 'D'  + roman_numeral(n - 500)
  in 400..499   then 'CD' + roman_numeral(n - 400)
  in 100..399   then 'C'  + roman_numeral(n - 100)
  in 90..99     then 'XC' + roman_numeral(n - 90)
  in 50..89     then 'L'  + roman_numeral(n - 50)
  in 40..49     then 'XL' + roman_numeral(n - 40)
  in 10..39     then 'X'  + roman_numeral(n - 10)

baweaver

# Pattern to match a link: <a/>  
node in { name: 'a' }

# Pattern for a link with a class: <a class="foo"/>
node in { name: 'a', class: 'foo' }

# Pattern to select that link: <a class="foo">{.}</a>
node => { name: 'a', class: 'foo', children: }

# Pattern to select the target URL: <a class="foo" href="{.}"/>

baweaver

require 'matchable'

class Person
  include Matchable

  deconstruct :new
  deconstruct_keys :name, :age

  attr_reader :name, :age

baweaver

class Card
  SUITS        = %w(S H D C).freeze
  RANKS        = %w(2 3 4 5 6 7 8 9 10 J Q K A).freeze
  RANKS_SCORES = RANKS.each_with_index.to_h

  include Comparable

  attr_reader :suit, :rank

  def initialize(suit, rank)