stack-lesson24.rb

class EmptyStackError < StandardError; end

class Stack
  def initialize
    @stack = []
    @size  = 0
  end

  def empty?
    @size == 0
  end

  def push(val)
    @size += 1
    @stack << val
  end

  def pop
    raise EmptyStackError if @stack.empty?
    @size -= 1
    @stack.pop
  end

  def size
    @size
  end
end