07 - delegating method calls to another object.rb

O Reilly Ruby Cookbook source code

require 'delegate'

# An integer represented as an ordinal number (1st, 2nd, 3rd...), as
# opposed to a cardinal number (1, 2, 3...) Generated by the
# DelegateClass to have all the methods of the Fixnum class.
class OrdinalNumber < DelegateClass(Fixnum)

  def to_s
    delegate_s = __getobj__.to_s
    check = abs
    if check == 11 or check == 12
      suffix = "th"
    else
      case check % 10
      when 1 then suffix = "st"
      when 2 then suffix = "nd"
      else suffix = "th"
      end
    end
    delegate_s + suffix
  end
end

4.to_s                                         # => "4"
OrdinalNumber.new(4).to_s                      # => "4th"

OrdinalNumber.new(102).to_s                    # => "102nd"
OrdinalNumber.new(11).to_s                     # => "11th"
OrdinalNumber.new(-21).to_s                    # => "-21st"

OrdinalNumber.new(5).succ                      # => 6
OrdinalNumber.new(5) + 6                       # => 11 
OrdinalNumber.new(5) + OrdinalNumber.new(6)     # => 11
#---
require 'forwardable'

class AppendOnlyArray
  extend Forwardable
  def initialize
    @array = []
  end

  def_delegator :@array, :<<
end

a = AppendOnlyArray.new
a << 4
a << 5
a.size
# NoMethodError: undefined method `size' for #<AppendOnlyArray:0xb7bf56f4 @array=[4, 5]>
#---
class RandomAccessHash 
  extend Forwardable
  def initialize
    @delegate_to = {}
  end

  def_delegators :@delegate_to, :[], "[]="
end

balances_by_account_number = RandomAccessHash.new

# Load balances from a database or something.
balances_by_account_number["101240A"] = 412.60
balances_by_account_number["104918J"] = 10339.94
balances_by_account_number["108826N"] = 293.01
#---
balances_by_account_number["104918J"]                   # => 10339.94
balances_by_account_number.each do |number, balance|
  puts "I now know the balance for account #{number}: it's #{balance}"
end
# NoMethodError: undefined method `each' for #<RandomAccessHash:0xb7be7298>
#---