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);