queue.lua

local Queue = Object:extend()
continuable.Queue = Queue

function Queue:initialize()
  self.head = {}
  self.tail = {}
  self.index = 1
  self.headLength = 0
end

function Queue:shift()
  if self.index > self.headLength then
    self.head, self.tail = self.tail, self.head
    self.index = 1
    self.headLength = #self.head
    if self.headLength == 0 then
      return
    end
  }
  local value = self.head[self.index]
  self.head[self.index] = nil
  self.index = self.index + 1
  return value
end

function Queue:push(item)
  return table.insert(self.tail, item)
end