Re: [boost] [Fusion] Tentative of trasnform_if failed :(

Subject: Re: [boost] [Fusion] Tentative of trasnform_if failed :(
From: Jeffrey Lee Hellrung, Jr. (jeffrey.hellrung_at_[hidden])
Date: 2011-04-19 15:30:22

On Tue, Apr 19, 2011 at 11:57 AM, Christopher Schmidt <
mr.chr.schmidt_at_[hidden]> wrote:

> falcou <Joel.Falcou_at_[hidden]> writes:
>
> > The following code
> >
> > http://ideone.com/xYk4X
> >
> > doesn't compile and i cant get the why of it.
> >
> > The goal is to have a fusion transform_if that takes a compile-time
> > predicates
> > For each element int he sequence, if the predicates its true, we apply
> > some
> > transform on it, if not we return the element unchanged.
> >
> > What am I missing ?
>
> The MPL lambda template type parameter of the functor that is passed to
> Fusion causes the trouble.  This functor is used by Fusion as a template
> type parameter for an internal metafunction class which turns into an
> (invalid) lambda expression due to the nested placeholder.  Making
> 'preds' a metafunction class, e.g. via mpl::quote1, should make your
> code compile fine.
>

Could this be considered a Boost.Fusion bug?  Seems like it would be
Boost.Fusion's job to insulate any template parameters it receives from
unintentional lambda substitution.  [I making this comment under the
assumption that I understand the problem, which may not be the case.]

- Jeff