From: Aleksey Gurtovoy (agurtovoy_at_[hidden])
Date: 2004-12-25 16:39:55
David Abrahams writes:
> Aleksey Gurtovoy wrote:
>
> >
> >>From http://www.boost.org/libs/mpl/doc/refmanual/protect.html:
> >
> > 'protect' is an identity wrapper for a Metafunction Class that
> > prevents its argument from being recognized as a bind expression.
> >
> > Actually, the above definition is incomplete; should be:
> >
> > 'protect' is an identity wrapper for a Metafunction Class that
> > prevents its argument from being recognized as a bind/placeholder
> > expression.
> >
> > The main usage for 'protect' is to prevent parametrized metafunction
> > classes from being accidentally treated as a placeholder expression
> > simply because their arguments happened to embed a placeholder.
>
> Hum. Seems a bit counterintuitive that protect doesn't apply equally
> well to this case.
??? As I tried to explain in my previous reply, 'protect' already has a
well-defined semantics in lambda expressions, and it's quite different
from what is needed to support "nested scopes". It would be nice to have
a single magic primitive that would work the way you want it to work
depending on the particular use case at hand, but I for one have no
knowledge of how to implement one.
-- Aleksey Gurtovoy MetaCommunications Engineering