Basic implementation of Enumerable.inject() in Ruby

injectable.rb

require 'rubygems'
require 'rspec'

module Enumerable
  def myinject (base = nil, &block)
    return nil if block.nil?
    return nil if self.length.zero?

    if base.nil?
      case self.first
      when Fixnum then base = 0
      when String then base = ''
      else return nil
      end
    end

    self.each do |e|
      base = block.call(base, e)
    end

    base
  end
end

describe Enumerable do
  describe '#myinject' do
    let(:arr) { Array(1..5) }
    let(:arr2) { %w(a b c) }

    it 'should return nil if no block exists' do
      arr.myinject{}.should == nil
    end

    it 'should return return 15 for accumulator + element' do
      arr.myinject(0){ |acc, e| acc + e }.should == 15
      arr.myinject{ |acc, e| acc + e }.should == 15
    end

    it 'should return aabaca for accumulator + element + a' do
      arr2.myinject{ |acc, e| acc + e + 'a'}.should == 'aabaca'
    end
  end
end