Re: [boost] [RFC] sticky_exception

From: Giovanni Piero Deretta (gpderetta_at_[hidden])
Date: 2007-09-18 04:32:27

On 9/13/07, Howard Hinnant <hinnant_at_[hidden]> wrote:
> I am requesting comments, both for and against a "sticky exception".
> [...]
> Do you see a use for such a class?  Would you use it?  Would you want
> libraries you're using to use it?  Do you have real world example
> conditions which fit this use case?  Or is it just evil (and why)?
>

I think it might be a little too much on the evil side. Wouldn't it
break otherwise exception safe (if admittedly not very elegant) code
like the following?

template<typename F>
bool foo(F f) {
   bar = acquire-resource-bar()
   bool failed = false;
   try {
       f();
   } catch (....) {
       failed = true;
   }
   release-resource-bar(bar);
   return failed;
}

Foo would work correctly for any function-like objects, except for
those that throw
sticky exception.

void baz() {
    sticky_exception s
    throw s;
}

int main() {
   foo(baz);  // XXX leaks a bar!!
}

That is, you can't throw a sticky exception unless everything in the
call stack is capable of handling it, else you might leak. I know that
the preferred idiom for exception safety is RAII (Which is also
sticky-exception-safe), but sometimes it is cumbersome to write a RAII
wrapper just for one use.

HTH,

gpd