| .. Sequences/Intrinsic Metafunctions//size |
| |
| size |
| ==== |
| |
| Synopsis |
| -------- |
| |
| .. parsed-literal:: |
| |
| template< |
| typename Sequence |
| > |
| struct size |
| { |
| typedef |unspecified| type; |
| }; |
| |
| |
| |
| Description |
| ----------- |
| |
| ``size`` returns the number of elements in the sequence, that is, the number of elements |
| in the range [``begin<Sequence>::type``, ``end<Sequence>::type``). |
| |
| |
| Header |
| ------ |
| |
| .. parsed-literal:: |
| |
| #include <boost/mpl/size.hpp> |
| |
| |
| |
| Model of |
| -------- |
| |
| |Tag Dispatched Metafunction| |
| |
| |
| Parameters |
| ---------- |
| |
| +---------------+-----------------------+-----------------------------------------------+ |
| | Parameter | Requirement | Description | |
| +===============+=======================+===============================================+ |
| | ``Sequence`` | |Forward Sequence| | A sequence to query. | |
| +---------------+-----------------------+-----------------------------------------------+ |
| |
| |
| Expression semantics |
| -------------------- |
| |
| |
| For any |Forward Sequence| ``s``: |
| |
| |
| .. parsed-literal:: |
| |
| typedef size<s>::type n; |
| |
| :Return type: |
| |Integral Constant|. |
| |
| :Semantics: |
| Equivalent to |
| |
| .. parsed-literal:: |
| |
| typedef distance< begin<s>::type,end<s>::type >::type n; |
| |
| |
| :Postcondition: |
| ``n::value >= 0``. |
| |
| |
| |
| Complexity |
| ---------- |
| |
| The complexity of the ``size`` metafunction directly depends on the implementation of |
| the particular sequence it is applied to. In the worst case, ``size`` guarantees a |
| linear complexity. |
| |
| If the ``s`` is a |Random Access Sequence|, ``size<s>::type`` is an |O(1)| operation. |
| The opposite is not necessarily true |--| for example, a sequence class that models |
| |Forward Sequence| might still give us an |O(1)| ``size`` implementation. |
| |
| |
| Example |
| ------- |
| |
| .. parsed-literal:: |
| |
| typedef list0<> empty_list; |
| typedef vector_c<int,0,1,2,3,4,5> numbers; |
| typedef range_c<int,0,100> more_numbers; |
| |
| BOOST_MPL_ASSERT_RELATION( size<list>::value, ==, 0 ); |
| BOOST_MPL_ASSERT_RELATION( size<numbers>::value, ==, 5 ); |
| BOOST_MPL_ASSERT_RELATION( size<more_numbers>::value, ==, 100 ); |
| |
| |
| See also |
| -------- |
| |
| |Forward Sequence|, |Random Access Sequence|, |empty|, |begin|, |end|, |distance| |
| |
| |
| .. 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) |