| .. Sequences/Intrinsic Metafunctions//has_key |
| |
| has_key |
| ======= |
| |
| Synopsis |
| -------- |
| |
| .. parsed-literal:: |
| |
| template< |
| typename Sequence |
| , typename Key |
| > |
| struct has_key |
| { |
| typedef |unspecified| type; |
| }; |
| |
| |
| |
| Description |
| ----------- |
| |
| Returns a true-valued |Integral Constant| if ``Sequence`` contains an element |
| with key ``Key``. |
| |
| |
| Header |
| ------ |
| |
| .. parsed-literal:: |
| |
| #include <boost/mpl/has_key.hpp> |
| |
| |
| Model of |
| -------- |
| |
| |Tag Dispatched Metafunction| |
| |
| |
| Parameters |
| ---------- |
| |
| +---------------+---------------------------+-----------------------------------------------+ |
| | Parameter | Requirement | Description | |
| +===============+===========================+===============================================+ |
| | ``Sequence`` | |Associative Sequence| | A sequence to query. | |
| +---------------+---------------------------+-----------------------------------------------+ |
| | ``Key`` | Any type | The queried key. | |
| +---------------+---------------------------+-----------------------------------------------+ |
| |
| |
| Expression semantics |
| -------------------- |
| |
| For any |Associative Sequence| ``s``, and arbitrary type ``key``: |
| |
| .. parsed-literal:: |
| |
| typedef has_key<s,key>::type c; |
| |
| :Return type: |
| Boolean |Integral Constant|. |
| |
| :Semantics: |
| ``c::value == true`` if ``key`` is in ``s``'s set of keys; otherwise |
| ``c::value == false``. |
| |
| |
| Complexity |
| ---------- |
| |
| Amortized constant time. |
| |
| |
| Example |
| ------- |
| |
| .. parsed-literal:: |
| |
| typedef map< pair<int,unsigned>, pair<char,long> > m; |
| BOOST_MPL_ASSERT_NOT(( has_key<m,long> )); |
| |
| typedef insert< m, pair<long,unsigned long> > m1; |
| BOOST_MPL_ASSERT(( has_key<m1,long> )); |
| |
| |
| See also |
| -------- |
| |
| |Associative Sequence|, |count|, |insert|, |erase_key| |
| |
| |
| .. 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) |