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    <pre><code>//This has a large number of steps, but I'm gonna post them all. This is all using native Lua 5 and the lua CAPI. int CreateInstanceOfT(lua_State* L) { new (lua_newuserdata(L, sizeof(T))) T(constructor args); return 1; } int CallSomeFuncOnT(lua_State* L) { if (lua_istable(L, 1)) { // If we're passed a table, get CData lua_getfield(L, 1, "CData"); lua_replace(L, 1); } if (!lua_touserdata(L, 1)) lua_error(L); // longjmp out. T&amp; ref = *(T*)lua_touserdata(L, 1); ref.SomeFunc(); // If you want args, I'll assume that you can pass them yourself return 0; } int main() { lua_State* L = luaL_newstate(); lua_pushcfunction(L, CreateInstanceOfT); lua_setglobal(L, "CreateInstanceOfT"); lua_pushcfunction(L, CallSomeFuncOnT); lua_setglobal(L, "CallSomeFuncOnT"); luaL_dofile(L, "something.lua"); lua_close(L); } -- Accompanying Lua code: semicolons are optional but I do out of habit. In something.lua function CreateCInstance() local Instance = { CData = CreateInstanceOfT(); SomeFunc = CallSomeFuncOnT; } return Instance; end local object = CreateCInstance(); object:SomeFunc(); // Calls somefunc. </code></pre> <p>I could post a great quantity of detail about how to make exposure easier, and how to make inheritance, and suchlike - and it'll need altering if you want to expose more than one T (I think the most common solution is a simple <code>struct { std::auto_ptr&lt;void&gt;, int type }</code> deal). But, it should be a starting point if you don't understand anything about this process.</p> <p>Bascally, first, we ask Lua to allocate some space (the userdata), then put T in it. When CallSomeFuncOnT comes up, first we ask it if we have a table (many Lua classes are based around tables, as they support object orientation, metatables, and such), and get the userdata out, which we then convert into a pointer to our object, and then convert into a reference. Remember that lua_touserdata gives you a void*, so you'd better be damn sure about what's on the other end. Then we call somefunc and return. In Main, we just register the functions as globals.</p> <p>Now, in Lua, when you call CreateInstanceOfT, it effectively just calls the T constructor, transparently to the Lua user. Then we ditch it in a table, which is simpler for Lua novices, and call SomeFunc by passing it this table. </p>
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    1. COMan, I can't believe how much this code sucks :P
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    2. COAm I wrong, or is it true that T's destructor never gets called using this technique? As I understand it, Lua doesn't know anything about C++ objects and simply calls `free` for memory it controls, such as that allocated by `lua_newuserdata`.
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