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

From: Daniel Walker (daniel.j.walker_at_[hidden])
Date: 2007-03-20 14:07:00

On 3/20/07, Eric Niebler <eric_at_[hidden]> wrote:
>
> Daniel Walker wrote:
> > On 3/20/07, Eric Niebler <eric_at_[hidden]> wrote:
> >> Daniel Walker wrote:
> >>> 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.
> >>
> >> IMO, you have this backwards. Rather than patch result_of to handle
> >> lambda, lambda function objects should be modified to follow the
> >> result_of convention. It's now standard, after all.
> >
> > Good point. I considered doing that, but didn't want to intrude on any
> > user code out there that follows the current Boost.Lamda convention.
> > Of course, I don't mind submitting a patch to Boost.Lambda as you
> > suggest if there's interest. That would help alleviate the problem of
> > having multiple return type conventions among Boost libraries. I could
> > also try to patch Fusion. Perhaps, my result_of patch could still be
> > useful for providing backwards compatibility for current Boost.Lambda
> > style user defined functors.
>
>
> If lambda functors had both sig<> and result<> nested templates, then it
> would Just Work without causing any back-compat problems.

That's true, but I was concerned about funtors defined by lambda
users. Currently, if a user wants to write a functor to be used in a
lambda expression, the user needs to supply a sig<> to tell lambda
what the functor's return type is.

Of course, users currently can't use these functors with result_of
anyway. So, I suppose no one's feelings will be hurt if result_of
doesn't support their current lambda compatible functors. And it's not
too imposing to demand that they modify their functors to conform to
the result_of standard, so long as they can still be used in lambda
expressions. I think I'll try to patch lambda. Thanks!

Daniel