if_

Synopsis

template <class C, class T, class F>
struct if_
{
  // unspecified
};

Description

Evaluates the nullary metafunction C, and when it returns a true logical value, if_ returns the result of the nullary metafunction T, when C returns false, if_ returns the result of the nullary metafunction F.

Header

#include <mpllibs/metamonad/if_.hpp>

Expression semantics

For any ct nullary metafunction evaluating to true, cf nullary metafunction evaluating to false and t, f nullary metafunctions the following are equivalent:

if_<ct, t, f>::type
t::type

if_<cf, t, f>::type
f::type

Example

MPLLIBS_METAFUNCTION(divide_if_not_zero, (A)(B))
((
  if_<
    boost::mpl::equal_to<boost::mpl::int_<0>, B>,
    A,
    boost::mpl::divides<A, B>
  >
));

Copyright Abel Sinkovics (abel at elte dot hu) 2011. Distributed under the Boost Software License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt

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