Re: [boost] [signals] usage of any_cast

From: Doug Gregor (dgregor_at_[hidden])
Date: 2005-10-12 13:43:36

Hi Andreas,

On Oct 12, 2005, at 10:57 AM, Andreas Pokorny wrote:
> We just stumbled across a small problem with Boost.Signals,
> while playing with the symbol visibility features of gcc-3.4 and
> gcc-4. That feature is still buggy, but it unveiled some strange
> code.

We've stumbled into this as well.

> The code is in signal_template.hpp:
>
>  template<typename Pair>
>  R operator()(const Pair& slot) const  {
>   F* target = const_cast<F*>(any_cast<F>(&slot.second));
>   return (*target)(BOOST_SIGNALS_BOUND_ARGS);
>  }
>
> I dont see why any_cast is used here at all. The type safety
> is guranteed by the interface of Boost.Signals, so I doubt that
> someone will be able to abuse the library. I believe the author
> of that code had the same in mind, since he did not test
> target != 0 before invoking the target. So in my opinion a
> simple reinterpret_cast should suffice here. It would also
> fix our issue, although that one is caused by gcc.

You're right. Our options are:

   1) Fix any_cast to compare typeid().name() instead of type_info 
objects
   2) Make an unsafe_any_cast that doesn't do the check
   3) Switch signals to use void*'s

For 1.33.1, I like #2 best because it affects the least amount of code. 
For 1.34.0 and beyond, #1 is probably our best bet so that others don't 
run into the same problem.

        Doug