lua-patterns/singleton.lua at master · floydawong/lua-patterns · GitHub

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local function Class(super)
    local obj = {}
    obj.__index = obj
    setmetatable(obj, super)

    function obj.new(...)
        if obj._instance then
            return obj._instance
        end

        local instance = setmetatable({}, obj)
        if instance.ctor then
            instance:ctor(...)
        end

        obj._instance = instance
        return obj._instance
    end

    return obj
end

local class = Class()
local a = class.new()
local b = class.new()
a.name = "Singleton Pattern"

print(a.name)
print(b.name)

---------------------------------------------------------------------------
-- OUTPUT
---------------------------------------------------------------------------
-- Singleton Pattern
-- Singleton Pattern