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Task/Stack/Ruby/stack-2.rb

@@ -0,0 +1,80 @@
+require 'forwardable'
+
+# A stack contains elements in last-in, first-out order.
+# Stack#push adds new elements to the top of the stack;
+# Stack#pop removes elements from the top.
+class Stack
+  extend Forwardable
+
+  # Creates a Stack containing _objects_.
+  def self.[](*objects)
+    new.push(*objects)
+  end
+
+  # Creates an empty Stack.
+  def initialize
+    @ary = []
+  end
+
+  # Duplicates a Stack.
+  def initialize_copy(obj)
+    super
+    @ary = @ary.dup
+  end
+
+  # Adds each object to the top of this Stack. Returns self.
+  def push(*objects)
+    @ary.push(*objects)
+    self
+  end
+  alias << push
+
+  ##
+  # :method: pop
+  # :call-seq:
+  #   pop -> obj or nil
+  #   pop(n) -> ary
+  #
+  # Removes an element from the top of this Stack, and returns it.
+  # Returns nil if the Stack is empty.
+  #
+  # If passing a number _n_, removes the top _n_ elements, and returns
+  # an Array of them. If this Stack contains fewer than _n_ elements,
+  # returns them all. If this Stack is empty, returns an empty Array.
+  nil
+
+  if ([].pop(0) rescue false)
+    # Ruby >= 1.8.7
+    def_delegator :@ary, :pop
+  else
+    # Ruby < 1.8.7
+    def pop(*args)  # :nodoc:
+      case len = args.length
+      when 0
+        @ary.pop
+      when 1
+        n = [@ary.length, args.first].min
+        @ary.slice!(-n, n)
+      else
+        raise ArgumentError, "wrong number of arguments (#{len} for 0..1)"
+      end
+    end
+  end
+
+  ##
+  # :method: empty?
+  # Returns true if this Stack contains no elements.
+  def_delegator :@ary, :empty?
+
+  ##
+  # :method: size
+  # Returns the number of elements in this Stack.
+  def_delegator :@ary, :size
+  alias length size
+
+  # Converts this Stack to a String.
+  def to_s
+    "#{self.class}#{@ary.inspect}"
+  end
+  alias inspect to_s
+end