| .. Iterators/Iterator Metafunctions//distance |20 |
| |
| distance |
| ======== |
| |
| Synopsis |
| -------- |
| |
| .. parsed-literal:: |
| |
| template< |
| typename First |
| , typename Last |
| > |
| struct distance |
| { |
| typedef |unspecified| type; |
| }; |
| |
| |
| |
| Description |
| ----------- |
| |
| Returns the distance between ``First`` and ``Last`` iterators, that is, an |
| |Integral Constant| ``n`` such that ``advance<First,n>::type`` is |
| identical to ``Last``. |
| |
| |
| Header |
| ------ |
| |
| .. parsed-literal:: |
| |
| #include <boost/mpl/distance.hpp> |
| |
| |
| Parameters |
| ---------- |
| |
| +---------------+---------------------------+-----------------------------------+ |
| | Parameter | Requirement | Description | |
| +===============+===========================+===================================+ |
| | ``First``, | |Forward Iterator| | Iterators to compute a | |
| | ``Last`` | | distance between. | |
| +---------------+---------------------------+-----------------------------------+ |
| |
| Model Of |
| -------- |
| |
| |Tag Dispatched Metafunction| |
| |
| |
| Expression semantics |
| -------------------- |
| |
| For any |Forward Iterator|\ s ``first`` and ``last``: |
| |
| .. parsed-literal:: |
| |
| typedef distance<first,last>::type n; |
| |
| :Return type: |
| |Integral Constant|. |
| |
| :Precondition: |
| [``first``, ``last``) is a valid range. |
| |
| :Semantics: |
| Equivalent to |
| |
| .. parsed-literal:: |
| |
| typedef iter_fold< |
| iterator_range<first,last> |
| , long_<0> |
| , next<_1> |
| >::type n; |
| |
| |
| :Postcondition: |
| ``is_same< advance<first,n>::type, last >::value == true``. |
| |
| |
| Complexity |
| ---------- |
| |
| Amortized constant time if ``first`` and ``last`` are |Random Access Iterator|\ s, |
| otherwise linear time. |
| |
| |
| Example |
| ------- |
| |
| .. parsed-literal:: |
| |
| typedef range_c<int,0,10>::type range; |
| typedef begin<range>::type first; |
| typedef end<range>::type last; |
| |
| BOOST_MPL_ASSERT_RELATION( (distance<first,last>::value), ==, 10); |
| |
| |
| See also |
| -------- |
| |
| |Iterators|, |Tag Dispatched Metafunction|, |advance|, |next|, |prior| |
| |
| |
| .. 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) |
