Object Orientation model for Lua

ObjectOrientation.lua

local setmetatable = setmetatable
local table, debug = table, debug

do --_G.class
    local function class_new(self, ...)
        return setmetatable({}, self)
    end
    _G.class = function(...)
        local supers = {...}
        local class = table.remove(supers, #supers)
        
        class.__index = (
                class.__index ~= nil and class.__index
            or  class.__index_def and class.__index_def(class)
            or  class
        )
        class[class] = true
        class.__init = class.__init or class_new
        
        local supers_len = #supers -- hopefully this will help LuaJIT unroll the loop statically
        return setmetatable(
            class,
            {
                __supers = supers,
                __class = class,
                __call = function(self, ...) return self.__init(self, ...) end,
                __index = (
                        supers_len == 0 and nil
                    or  supers_len == 1 and supers[1]
                    or  function(self, key)
                            for super_i = 1, supers_len do
                                local value = supers[super_i][key]
                                if value then return value end
                            end
                        end
                ),
            }
        )
    end
end
do _G.classof
    = debug.getmetatable -- hopefully this aliasing doesn't mess up the fast function optimisation
end
do _G.instanceof
    = function(instance, class)
        local mt = debug.getmetatable(instance)
        return mt and mt[class]
    end
end
do _G.supersof
    = function(class)
        return debug.getmetatable(class).__supers
    end
end
do _G.supersofinstance -- == supersof(classof(instance))
    = function(instance)
        return debug.getmetatable(debug.getmetatable(instance)).__supers
    end
end