From: Aleksey Gurtovoy (agurtovoy_at_[hidden])
Date: 2003-09-05 15:26:18
Jaakko Jarvi wrote:
> Hi,
Hi Jaakko,
>
> We're writing enable_if docs and have a question about MPL. The docs
> do not seem to mention metafunctions like not_ or and_;
Hmm, http://www.boost.org/libs/mpl/doc/ref/Reference/not.html?
> we can find
> logical_not, logical_and, etc. which seem to be applying to functions,
> not values.
'logical_not/_and/_or' were the old spellings; perhaps you are looking at
the old docs?
>
> So assuming we have:
>
> class A { static const bool value = true; };
>
> What is the right way to get the inverse of A::value as an MPL wrapped
> boolean?
Well, as everything else in the library that works with integral values,
'not_' expects its argument to be a model of a bool integral constant - that
is, 'A' should be
class A {
static const bool value = true; // for convenience only
typedef mpl::bool_<value> type;
};
Given that, yes, 'mpl::not_<A>' is the right way.
> PS. The reference manual was a bit hard to find, as the link was not
> in the table of contents of the main MPL documentation page.
Yes, it definitely needs fixing.
Thanks,
Aleksey