Re: Lua error handling and C++
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- Subject: Re: Lua error handling and C++
- From: Sam Roberts <sroberts@...>
- Date: 2006年10月16日 15:13:20 -0700
On Mon, Oct 16, 2006 at 05:05:45PM -0400, Glenn Maynard wrote:
> That means every object that I might want to create inside a binding
Not every object.
> needs to be handled in this way. Unfortunately, "delete p" where p is
> a void* will not call destructors--that would make it easy. I'm not
> a big fan of the "give everything in the world a base class" paradigm ...
Probably no way to avoid the tedium, but I'm not sure if you understood.
Create a single user-data that contains a pointer to a struct MyArgs {
std::string localA; std::string localB; }, and with a __gc pointing to a
function that calls delete on (struct MyArgs*) when the UD is
collected, the struct members will be destroyed.
Basically, this is a process of taking your stack variables, and putting
them on the heap, wrapped in a UD, so lua can tell you when to destroy
them, longjmp or no longjmp. Example is here:
http://www.lua.org/pil/29.1.html
but instead of having a DIR object, have a struct MyArgs, and instead of
calling opendir() call new MyArgs, and instead of calling closedir(),
call delete.
This may be tedious, but it is easy to be confident its "correct". C++
takes care of calling the dtors for all struct members, you make sure
that you call delete once in the __gc metamethods correctly, and lua
makes sure that the __gc metamethod is called. Since there is nothing on
the stack that is a leakable resource, there is nothing on the stack
that can be leaked. Also, "local" variables get freed the same way
error() or not, when lua cleans up the the lua->C stack.
You asked for suggestions on "other ways", this is one other way.
Cheers,
Sam
> > Its hard to have the benefits of C++ automatic resource freeing with
> > exceptions, without paying the costs for exceptions!
>
> Not at all.
What does that mean?
If you have way of getting automatic resource freeing across longjmp
without paying the cost for exceptions, why does this thread exist?