DictionaryLength.lua

Dict = {}
function Dict.__newindex(table, key, value)
    if value ~= nil and table.__INNER[key] == nil then
        table.__LENGTH = table.__LENGTH + 1
    elseif value == nil and table.__INNER[key] ~= nil then
        table.__LENGTH = table.__LENGTH - 1
    end
    rawget(table,"__INNER")[key] = value
end

function Dict.__index(table, key)
    return rawget(table, "__INNER")[key]
end
function Dict.__len(table)
    return rawget(table,"__LENGTH")
end


function dict()
    return setmetatable({__INNER = {}, __LENGTH = 0}, Dict)
end

myDictionary = dict()

myDictionary["hello"] = "world"
myDictionary["world"] = "!"
myDictionary["world"] = "?"
print(#myDictionary)
myDictionary["world"] = nil
print(#myDictionary)

print(myDictionary.hello)
print(myDictionary.world)