Re: Lua <-> C++ integration with "unused" stack slots
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- Subject: Re: Lua <-> C++ integration with "unused" stack slots
- From: Philipp Janda <siffiejoe@...>
- Date: 2010年2月04日 23:03:05 +0100
Am 04.02.2010 22:10, schrieb Oliver Schmidt:
> Hello list!
Hi!
>
> One possible way for integrating Lua with C++ code is to build a C++
> class that represent a Lua variable and manages its corresponding
> stack slot.
>
> C++ objects of this class type are holding their stack index and are
> responsible for releasing the corresponding stack slot on destruction
> (e.g. using the function lua_remove).
Why are you doing that? You don't get deterministic cleanup of Lua
values anyway, and IIRC, the stack slots are removed when the function
returns.
>
> This works well as long as objects are destructed in reverse order
> of their constructions, which is normally the case, e.g.
>
> class C
> {...};
>
> void f(C c1)
> {
> C c2;
> C c3;
> } // <- destruction order: c3, c2, c1
>
>
> But in some cases the destruction order may change, especially for
> temporary objects, e.g.
>
> C g()
> {
> C c1;
> return C(); // c1 is destructed before this temporary object
> } // is destroyed (at least with g++)
>
> The problem here is that removing a stack index that is not on the top
> shifts all stack slots above down.
>
> To solve this problem it would be fine if Lua supported "unused" stack
> indices.
It does (sort of): Use lua_pushnil + lua_replace instead of lua_remove.
>
> [...]
>
> Best regards,
> Oliver
>
Philipp