RE: std::exception Interoperability

["Erik Cassel" <erik@...>]

> Any time I see a catch(...), I start worrying

Agreed. If you look at the 5.1 code you'll see that Lua throws a
lua_longjmp*.  Therefore, I think that Lua should only catch a lua_longjmp*
and not a "...".  Any other exception thrown within luaD_rawrunprotected
should be considered a programming error.

As an alternative to my more generic patch (posted earlier), here is a very
small patch (untested) that I think addresses the (...) issue only:

#define LUAI_TRY(L,c,a)	\
	try
	{
		a 
	}
	catch(lua_longjmp*)
	{
		if ((c)->status == 0) 
			(c)->status = -1;
	}
	catch(...)
	{
		// Serious design error. Implementers are required to
		// throw *only* lua_longjmp*.

		// At this point we have no idea if the Lua stack has
		// an error message on it, and we don't know if (c)->status
		// is valid. All bets are off.

		// Pick your action  :-)
		assert(false);
		exit(-1);
		throw;
	}
	


-Erik




-----Original Message-----
From: lua-bounces@bazar2.conectiva.com.br
[mailto:lua-bounces@bazar2.conectiva.com.br] On Behalf Of Greg Falcon
Sent: Friday, March 24, 2006 2:56 PM
To: Lua list
Subject: Re: std::exception Interoperability

Any time I see a catch(...), I start worrying, so I'd love to get a
look at your improvements to the exception handling.

Greg F

On 3/24/06, Erik Cassel <erik@roblox.com> wrote:
>
> I have patched Lua 5.1 to seamlessly work with std::exception.
>
> This lets me throw an std::exception-derived object from anywhere in C++
> code. Lua will catch it and translate it appropriately in
> luaD_rawrunprotected().
>
> Also, Lua uses an std::exception-derived class to throw Lua errors. This
> means I can catch errors thrown by Lua (as in lua_touserdata).
>
>
> The benefits of this approach are:
>
> 1)      I don't have to write exception handlers in every entry point in
my
> code. If my code is based on std/boost then I can be confident that
> exceptions thrown by my code will be handled by Lua. I don't have to
> translate them into lua_error() calls.
>
> 2)      It is perfectly safe for me to intercept an exception thrown by
Lua.
> Since Lua now throws std::exception-derived objects I can catch and
inspect
> errors with a catch(std::exception&) clause. Moreover, if I decide *not*
to
> re-throw the exception, then Lua automatically pops the error message from
> the stack.
>
>
> Has anybody else done something like this?  Would it be useful to anybody?
> Have I missed something?
>
> I'd be happy to post my patch (and go over implementation details) and/or
> show some sample code of how it can be used.
>
> -Erik
>
>
>