| .. Sequences/Intrinsic Metafunctions//empty |
| |
| empty |
| ===== |
| |
| Synopsis |
| -------- |
| |
| .. parsed-literal:: |
| |
| template< |
| typename Sequence |
| > |
| struct empty |
| { |
| typedef |unspecified| type; |
| }; |
| |
| |
| |
| Description |
| ----------- |
| |
| Returns an |Integral Constant| ``c`` such that ``c::value == true`` if |
| and only if the sequence is empty. |
| |
| |
| Header |
| ------ |
| |
| .. parsed-literal:: |
| |
| #include <boost/mpl/empty.hpp> |
| |
| |
| Model of |
| -------- |
| |
| |Tag Dispatched Metafunction| |
| |
| |
| Parameters |
| ---------- |
| |
| +---------------+-----------------------+-----------------------------------+ |
| | Parameter | Requirement | Description | |
| +===============+=======================+===================================+ |
| | ``Sequence`` | |Forward Sequence| | A sequence to test. | |
| +---------------+-----------------------+-----------------------------------+ |
| |
| |
| Expression semantics |
| -------------------- |
| |
| For any |Forward Sequence| ``s``: |
| |
| |
| .. parsed-literal:: |
| |
| typedef empty<s>::type c; |
| |
| :Return type: |
| Boolean |Integral Constant|. |
| |
| :Semantics: |
| Equivalent to ``typedef is_same< begin<s>::type,end<s>::type >::type c;``. |
| |
| :Postcondition: |
| ``empty<s>::value == ( size<s>::value == 0 )``. |
| |
| |
| |
| Complexity |
| ---------- |
| |
| Amortized constant time. |
| |
| |
| Example |
| ------- |
| |
| .. parsed-literal:: |
| |
| typedef range_c<int,0,0> empty_range; |
| typedef vector<long,float,double> types; |
| |
| BOOST_MPL_ASSERT( empty<empty_range> ); |
| BOOST_MPL_ASSERT_NOT( empty<types> ); |
| |
| |
| See also |
| -------- |
| |
| |Forward Sequence|, |Integral Constant|, |size|, |begin| / |end| |
| |
| |
| .. 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) |
