Stack を簡易的に作る

stack.rb

class Stack
  attr_reader :stack
  
  def initialize
    @stack = []
  end

  def push(element)
    @stack.push(element)
  end

  def pop
    pop_value = @stack.first

    @stack.delete_at(0)

    pop_value
  end

  def peek
    @stack.first
  end

  def empty?
    @stack.empty?
  end

  def size
    @stack.size
  end
end

s = Stack.new
s.push("a")
s.push("b")

s.pop #=> a
s.stack #=> ["b"]
s.peek #=> b
s.empty? #=> false
s.size #=> 2