map = {}
local this = map


function clone(object)
    local lookup_table = {}
    local function _copy(object)
        if type(object) ~= "table" then
            return object
        elseif lookup_table[object] then
            return lookup_table[object]
        end
        local newObject = {}
        lookup_table[object] = newObject
        for key, value in pairs(object) do
            newObject[_copy(key)] = _copy(value)
        end
        return setmetatable(newObject, getmetatable(object))
    end
    return _copy(object)
end
function this:new()
    o = {}
    setmetatable(o,self)
    self.__index = self
    self.count = 0
    return o
end

function this:insert(k,v)
    if nil == self[k] then
        self[k] = clone(v)
        self.count = self.count + 1
    end
end


function this:remove(k)
    if nil ~= self[k] then
        self[k] = nil
        if self.count >0 then
            self.count = self.count - 1
        end
    end
end

function this:getpair(k)
    local value = nil
    if nil ~= self[k] then
        value = self[k]
    end
    return value
end

function  this:clear()
    for k,_ in pairs(self) do
        if nil ~= self[k] then
            self[k] = nil
        end
    end
    self.count = 0
end