Re: [boost] [utility] result_of and lambda patch

From: Daniel Walker (daniel.j.walker_at_[hidden])
Date: 2007-03-20 12:51:17

On 3/20/07, Giovanni Piero Deretta <gpderetta_at_[hidden]> wrote:
> On 3/20/07, Daniel Walker <daniel.j.walker_at_[hidden]> wrote:
> > Hello,
> >
> > I noticed that result_of doesn't handle functors created by the Boost
> > Lambda Library.
> > [...]
> > Among Boost libraries, there are at least two ways for function
> > objects to expose return types that are dependent on the types of
> > their arguments.
> >
> > 1) result_of instructs users to expose a template result<F(ARG1, ..., ARGN)>.
> > 2) Boost.Lambda instructs users to expose a template sig<tuple<ARG1,
> > ..., ARGN>, and it also uses this convention internally.
> >
> One more:
>
> 3) Fusion instruct users to expose a template result<ARG1... ARGN>.
>
> But I guess it is not easy to distinguish this case from 1).

Thanks. I wasn't aware of this case. I was afraid there may be other
conventions out there. I believe Boost.Typeof would handle the Fusion
case as well as any future conventions adopted by future libraries.
Still, for compilers that Boost.Typeof doesn't support, it would be
nice if result_of could handle Boost.Lambda at least. More recent
libraries and future libraries could consider adopting a previously
existing practice (result<F(Args) or sig<tuple<Args> >) that result_of
can support without typeof.

Daniel