Simple Queue/List Class

-- Copyright (c) 2015, Franco Sauvisky
-- All rights reserved.

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-- Simple queue/list class:

-- It might be useful to change the popleft and popright errors to "return
-- nil", depending on how you use it (if having nil elements is permitted).

local List = {begin = 0, final = 1}

function List:new()
    local newlist = {}
    setmetatable(newlist,self)
    self.__index = self
    return newlist
end

function List:pushleft(value)
    self[self.begin] = value
    self.begin = self.begin - 1
end

function List:pushright(value)
    self[self.final] = value
    self.final = self.final + 1
end

function List:popright()
    if self.final == self.begin + 1 then
        error("No element to pop") -- Or return nil?
    end

    local value = self[self.final - 1]
    self[self.final] = nil
    self.final = self.final - 1
    return value
end

function List:popleft()
    if self.begin == self.final - 1 then
        error("No element to pop") -- Or return nil?
    end

    local value = self[self.begin + 1]
    self[self.begin] = nil
    self.begin = self.begin + 1
    return value
end

return List