range.rb

class Range
  ##
  # call-seq:
  #    rng.first    -> obj
  #    rng.first(n) -> an_array
  #
  # Returns the first object in the range, or an array of the first +n+
  # elements.
  #
  #   (10..20).first     #=> 10
  #   (10..20).first(3)  #=> [10, 11, 12]
  #
  def first(*args)
    return self.begin if args.empty?

    raise ArgumentError, "wrong number of arguments (given #{args.length}, expected 1)" unless args.length == 1
    nv = args[0]
    raise TypeError, "no implicit conversion from nil to integer" unless nv.nil?.!
    raise TypeError, "no implicit conversion of #{nv.class} into Integer" unless nv.respond_to?(:to_int)
    n = nv.to_int
    raise TypeError, "no implicit conversion of #{nv.class} into Integer" unless n.kind_of?(Integer)
    raise ArgumentError, "negative array size (or size too big)" unless 0 <= n
    ary = []
    each do |i|
      break if n <= 0
      ary.push(i)
      n -= 1
    end
    ary
  end
end