tasks a-s

Task/Queue-Definition/Ruby/queue-definition-1.rb

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+require 'forwardable'
+
+# A FIFO queue contains elements in first-in, first-out order.
+# FIFO#push adds new elements to the end of the queue;
+# FIFO#pop or FIFO#shift removes elements from the front.
+class FIFO
+  extend Forwardable
+
+  # Creates a FIFO containing _objects_.
+  def self.[](*objects)
+    new.push(*objects)
+  end
+
+  # Creates an empty FIFO.
+  def initialize; @ary = []; end
+
+  # Appends _objects_ to the end of this FIFO. Returns self.
+  def push(*objects)
+    @ary.push(*objects)
+    self
+  end
+  alias << push
+  alias enqueue push
+
+  ##
+  # :method: pop
+  # :call-seq:
+  #   pop -> obj or nil
+  #   pop(n) -> ary
+  #
+  # Removes an element from the front of this FIFO, and returns it.
+  # Returns nil if the FIFO is empty.
+  #
+  # If passing a number _n_, removes the first _n_ elements, and returns
+  # an Array of them. If this FIFO contains fewer than _n_ elements,
+  # returns them all. If this FIFO is empty, returns an empty Array.
+  def_delegator :@ary, :shift, :pop
+  alias shift pop
+  alias dequeue shift
+
+  ##
+  # :method: empty?
+  # Returns true if this FIFO contains no elements.
+  def_delegator :@ary, :empty?
+
+  ##
+  # :method: size
+  # Returns the number of elements in this FIFO.
+  def_delegator :@ary, :size
+  alias length size
+
+  # Converts this FIFO to a String.
+  def to_s
+    "FIFO#{@ary.inspect}"
+  end
+  alias inspect to_s
+end