make_tmp_value

Synopsis

template <class T, class Tag>
struct make_tmp_value
{
  typedef T type;

  // unspecified
};

Description

When a class is used as a value for template metaprograms, it needs to behave as a nullary metafunction evaluating to itself to avoid issues when it is passed to lazy metafunctions. This metafunction can be used to add ::type and optionally ::tag to a type that doesn't have one.

Header

#include <mpllibs/metamonad/make_tmp_value.hpp>

Expression semantics

For any t and v types the following are equivalent:

make_tmp_value<t>::type
make_tmp_value<t>

tmp_value<t, v>::type
tmp_value<t, v>

tmp_value<t, v>::tag
v

For any t and v types make_tmp_value<t> and make_tmp_value<t, v> publicly inherit from t.

Example

make_tmp_value<boost::mpl::always<int>>

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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