Below is a Lua-only version. In C you would typically declare a static
variable and use a pointer to it as the ID.
-- Put this in MyObject.lua, then require'MyObject'.
-- MyObject.new() is the factory.
local getmetatable = getmetatable
local setmetatable = setmetatable
local type = type
module('MyObject')
local ID = {} -- In C, use a pointer &ID for static int ID;
local MT = { __id = ID }
function new()
return setmetatable({}, MT)
end
function isValid(self)
local mt = getmetatable(self or {})
return (mt ~= nil) and (mt.__id == ID)
end
-- Test run:
Lua 5.1.4 Copyright (C) 1994-2008 Lua.org, PUC-Rio
> require'MyObject'
> obj=MyObject.new()
> print(MyObject.isValid(obj))
true
> print(MyObject.isValid({}))
false
Thanks for the example, but I don't understand how it relates to my original question. I would like to define the plugin interface similar to a C++ abstract base class. If an object is derived from the base class you know the methods which are available for the host to call.
In this example, how I understand it, you do an id check in order to know if an object is really the object you expect it to be, but I don't understand where you would define its interface.
Thijs
