| .. Metafunctions/Concepts//Trivial Metafunction |70 |
| |
| Trivial Metafunction |
| ==================== |
| |
| Description |
| ----------- |
| |
| A |Trivial Metafunction| accepts a single argument of a class type ``x`` and |
| returns the ``x``\ 's nested type member ``x::name``, where ``name`` is |
| a placeholder token for the actual member's name accessed by a specific |
| metafunction's instance. By convention, all `trivial metafunctions`__ in MPL |
| are named after the members they provide assess to. For instance, a |Trivial |
| Metafunction| named ``first`` reaches for the ``x``\ 's nested member |
| ``::first``. |
| |
| __ `Trivial Metafunctions Summary`_ |
| |
| |
| Expression requirements |
| ----------------------- |
| |
| |In the following table...| ``name`` is placeholder token for the names of |
| the |Trivial Metafunction| itself and the accessed member, and ``x`` is |
| a class type such that ``x::name`` is a valid *type-name*. |
| |
| +---------------------------+-------------------+---------------------------+ |
| | Expression | Type | Complexity | |
| +===========================+===================+===========================+ |
| | ``name<x>::type`` | Any type | Constant time. | |
| +---------------------------+-------------------+---------------------------+ |
| |
| |
| Expression semantics |
| -------------------- |
| |
| .. parsed-literal:: |
| |
| typedef name<x>::type r; |
| |
| :Precondition: |
| ``x::name`` is a valid *type-name*. |
| |
| :Semantics: |
| ``is_same<r,x::name>::value == true``. |
| |
| |
| Models |
| ------ |
| |
| * |first| |
| * |second| |
| * |base| |
| |
| |
| See also |
| -------- |
| |
| |Metafunctions|, |Trivial Metafunctions|, |identity| |
| |
| |
| .. copyright:: Copyright © 2001-2009 Aleksey Gurtovoy and David Abrahams |
| 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) |
