gistfile1.txt

class Array
  def skip_first?(accumulator)
    return 1 if accumulator.nil?
    return 0 unless accumulator.nil?
  end

  def my_inject(accumulator = nil)
    start = skip_first? accumulator
    accumulator ||= self.first

    if block_given?
      self[start..-1].each do |number|
        accumulator = yield(accumulator,number)
      end
    end
    accumulator
  end
end

describe "my inject method" do
  context 'when there is less than two elements with no initial accumulator' do
    it "empty array be nil" do
      expect([].my_inject).to eq [].inject
    end
    it "single array should return it's element" do
      expect([0].my_inject).to eq [0].inject
    end
  end

  context 'where there is 3 or more elements with no initial accumulator' do
    it "uses the first element as the seed" do
      sum = lambda {|sum,number| sum + number }
      expect([1,2,3].my_inject &sum).to eq [1,2,3].inject &sum
    end
  end

  context 'where there is 2 or more elements with an initial accumulator' do
    it "uses the first element as the seed" do
      result =  [1,2,3].my_inject(100) {|sum,number| sum + number }
      expected =  [1,2,3].inject(100) {|sum,number| sum + number }
      expect(result).to eq expected
    end
  end

end