The MPL Reference Manual: distance

distance

template<
      typename First
    , typename Last
    >
struct distance
{
    typedef unspecified type;
};

Returns the distance between First and Last iterators, that is, an Integral Constant n such that advance::type is identical to Last.

#include <boost/mpl/distance.hpp>

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

For any Forward Iterators first and last:

typedef distance::type n;

Return type:	Integral Constant.
Precondition:	[`first`, `last`) is a valid range.
Semantics:	Equivalent to typedef iter_fold< iterator_range , long_<0> , next<_1> >::type n;
Postcondition:	`is_same< advance::type, last >::value == true`.

Amortized constant time if first and last are Random Access Iterators, otherwise linear time.

typedef range_c::type range;
typedef begin::type first;
typedef end::type last;

BOOST_MPL_ASSERT_RELATION( (distance::value), ==, 10);

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