my_map.rb

class Array
  def my_map(&prc)
    new = []
    self.my_each{|item| new << prc.call(item)}
    new
  end

  def my_select(&prc)
    selected = []
    self.my_each{|item| selected << item if prc.call(item)}
    selected
  end

  def my_inject(&blk)
    sum = self[0]
    self[1..-1].my_each{|item| sum = blk.call(sum, item) }
    sum
  end
end