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source: downloads/boost_1_33_1/libs/mpl/doc/src/refmanual/advance.rst @ 12

Last change on this file since 12 was 12, checked in by landauf, 17 years ago

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advance

Synopsis

template<
      typename Iterator
    , typename N
    >
struct advance
{
    typedef |unspecified| type;
};

Description

Moves Iterator by the distance N. For `bidirectional`_ and `random access`_ iterators, the distance may be negative.

Parameters

Parameter Requirement Description
Iterator |Forward Iterator| An iterator to advance.
N |Integral Constant| A distance.

Expression semantics

For a |Forward Iterator| iter and arbitrary |Integral Constant| n:

typedef advance<iter,n>::type j;
Return type:

|Forward Iterator|.
Precondition:

If Iterator is a |Forward Iterator|, n::value must be nonnegative.
Semantics:

Equivalent to:

typedef iter i0;
typedef next<i0>::type i1;
|...|
typedef next<in-1>::type j;

if n::value > 0, and

typedef iter i0;
typedef prior<i0>::type i1;
|...|
typedef prior<in-1>::type j;

otherwise.
Postcondition:

j is dereferenceable or past-the-end; distance<iter,j>::value == n::value if n::value > 0, and distance<j,iter>::value == n::value otherwise.

Complexity

Amortized constant time if iter is a model of |Random Access Iterator|, otherwise linear time.

Example

typedef range_c<int,0,10> numbers;
typedef begin<numbers>::type first;
typedef end<numbers>::type last;
typedef advance<first,int_<10> >::type i1;
typedef advance<last,int_<-10> >::type i2;
BOOST_MPL_ASSERT(( boost::is_same<i1,last> ));
BOOST_MPL_ASSERT(( boost::is_same<i2,first> ));

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