Does Ruby have containers like stacks, queues, linked-lists, maps, or sets?

(Moved from Comment)

Well, an array can be a stack or queue by limiting yourself to stack or queue methods (push, pop, shift, unshift). Using push / pop gives LIFO(last in first out) behavior (stack), while using push / shift or unshift / pop gives FIFO behavior (queue).

Maps are hashes, and a Set class already exists.

You could implement a linked list using classes, but arrays will give linked-list like behavior using the standard array methods.

I guess most of it is covered in above answers but just for summing it up for a better explanation:

Stack:

stack = []
stack << 2 # push 2 => stack = [2]
stack << 3 # push 3 => stack = [2, 3]
stack.pop  # pop => 3, stack = [2]

Queue:

# we have a Queue class
queue = Queue.new
queue << 2 # push 2 => queue = [2]
queue << 3 # push 3 => queue = [2, 3] (just a representation, it will be an object though)
queue.pop # pop 2

Linked List:

# A very simple representation
class Node
  attr_accessor :value, :next_node

  def initialize(value, next_node=nil)
    @value = value
    @next_node = next_node
  end
end

class LinkedList

  def initialize(value)
    @head = Node.new(value)
  end

  def add(value)
    current = @head
    while !current.next_node.nil?
      current = current.next_node
    end
    current.next_node = Node.new(value)
  end
end

ll = LinkedList.new
ll.add(10)
ll.add(20)

Maps:

# Hash incase of ruby
a = {} (or a = Hash.new)
a['one'] = 1 # a = {"one"=>1}
a['two'] = 2 # a = {"one"=>1, "two"=>2}

Set:

# we have a Set class
require 'set'
s = Set.new         # <Set: {}>
s.add(1)            # <Set: {1}>
s.add(2)            # <Set: {1, 2}>
s.add(1)            # <Set: {1, 2}>
s.instance_of?(Set) # true