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distance

Synopsis

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

#include <boost/mpl/distance.hpp>

Parameters

Parameter Requirement Description
First, Last Forward Iterator Iterators to compute a distance between.

Model Of

Tag Dispatched Metafunction

Expression semantics

For any Forward Iterators first and last:

typedef distance<first,last>::type n;
Return type:

Integral Constant.

Precondition:

[first, last) is a valid range.

Semantics:

Equivalent to

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 Iterators, otherwise linear time.

Example

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