| .. Metafunctions/Logical Operations//or_ |20 |
| |
| or\_ |
| ==== |
| |
| Synopsis |
| -------- |
| |
| .. parsed-literal:: |
| |
| template< |
| typename F1 |
| , typename F2 |
| |...| |
| , typename F\ *n* = |unspecified| |
| > |
| struct or\_ |
| { |
| typedef |unspecified| type; |
| }; |
| |
| |
| |
| Description |
| ----------- |
| |
| Returns the result of short-circuit *logical or* (``||``) operation on its arguments. |
| |
| |
| Header |
| ------ |
| |
| .. parsed-literal:: |
| |
| #include <boost/mpl/or.hpp> |
| #include <boost/mpl/logical.hpp> |
| |
| |
| Parameters |
| ---------- |
| |
| +---------------+---------------------------+-----------------------------------------------+ |
| | Parameter | Requirement | Description | |
| +===============+===========================+===============================================+ |
| | |F1...Fn| | Nullary |Metafunction| | Operation's arguments. | |
| +---------------+---------------------------+-----------------------------------------------+ |
| |
| |
| Expression semantics |
| -------------------- |
| |
| For arbitrary nullary |Metafunction|\ s |f1...fn|: |
| |
| .. parsed-literal:: |
| |
| typedef or_<f1,f2,\ |...|\ ,f\ *n*\>::type r; |
| |
| :Return type: |
| |Integral Constant|. |
| |
| :Semantics: |
| ``r`` is ``true_`` if either of ``f1::type::value``, ``f2::type::value``,... |
| ``fn::type::value`` expressions evaluates to ``true``, and ``false_`` otherwise; |
| guarantees left-to-right evaluation; the operands subsequent to the first |
| ``f``\ *i* metafunction that evaluates to ``true`` are not evaluated. |
| |
| .. .......................................................................... |
| |
| .. parsed-literal:: |
| |
| typedef or_<f1,f2,\ |...|\ ,f\ *n*\> r; |
| |
| :Return type: |
| |Integral Constant|. |
| |
| :Semantics: |
| Equivalent to |
| |
| .. parsed-literal:: |
| |
| struct r : or_<f1,f2,\ |...|\ ,f\ *n*\>::type {}; |
| |
| |
| Example |
| ------- |
| |
| .. parsed-literal:: |
| |
| struct unknown; |
| |
| BOOST_MPL_ASSERT(( or_< true\_,true\_ > )); |
| BOOST_MPL_ASSERT(( or_< false\_,true\_ > )); |
| BOOST_MPL_ASSERT(( or_< true\_,false\_ > )); |
| BOOST_MPL_ASSERT_NOT(( or_< false\_,false\_ > )); |
| BOOST_MPL_ASSERT(( or_< true\_,unknown > )); // OK |
| BOOST_MPL_ASSERT(( or_< true\_,unknown,unknown > )); // OK too |
| |
| |
| See also |
| -------- |
| |
| |Metafunctions|, |Logical Operations|, |and_|, |not_| |
| |
| |
| .. 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) |