class Array
  def my_each
    c = 0
    until c == size
      yield(self[c])
      c += 1
    end
    self
  end

  def my_map
    p self.inspect
    acc = []
    my_each { |a| acc << yield(a) }
    p acc
  end
end
names = [ "david", "black", "foo" ]
names.my_map { |name| name.upcase }