std::experimental::ranges::distance

 

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Readable Writable WeaklyIncrementable Incrementable	Iterator Sentinel SizedSentinel	InputIterator ForwardIterator BidirectionalIterator RandomAccessIterator	OutputIterator
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iter_move iter_swap	advance distance	next prev
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istream_iterator	ostream_iterator	istreambuf_iterator	ostreambuf_iterator

 

Defined in header <experimental/ranges/iterator>
namespace {     constexpr /* unspecified */ distance = /* unspecified */; }		(ranges TS) (customization point object)
Call signature
template< Iterator I, Sentinel<I> S > constexpr ranges::difference_type_t<I> distance( I first, S last );	(1)
template< Range R > constexpr ranges::difference_type_t<ranges::iterator_t<R>> distance( R&& r );	(2)
template< SizedRange R > constexpr ranges::difference_type_t<ranges::iterator_t<R>> distance( R&& r );	(3)

Returns the distance between first and last, or between the beginning and the end of the range r.

1) If SizedSentinel<S, I> is satisfied, equivalent to return last - first;. Otherwise, returns the number of increments needed to get from first to last. If [first, last) does not denote a range, then I and S must be the same type and must model SizedSentinel, and [last, first) must denote a range. Otherwise, the behavior is undefined.

2) Equivalent to return ranges::distance(ranges::begin(r), ranges::end(r));.

3) Equivalent to return ranges::size(r);.

Instantiating overloads (2,3) may be ill-formed if the header <experimental/ranges/range> is not included before the point of instantiation.

Customization point objects

The name ranges::distance denotes a customization point object, which is a function object of a literal Semiregular class type (denoted, for exposition purposes, as DistanceT). All instances of DistanceT are equal. Thus, ranges::distance can be copied freely and its copies can be used interchangeably.

Given a set of types Args..., if std::declval<Args>()... meet the requirements for arguments to ranges::distance above, DistanceT will satisfy ranges::Invocable<const DistanceT, Args...>. Otherwise, no function call operator of DistanceT participates in overload resolution.

In every translation unit in which ranges::distance is defined, it refers to the same instance of the customization point object. (This means that it can be used freely in things like inline functions and function templates without violating the one-definition rule.)

Return value

The distance between first and last, or between the beginning and the end of the range r.

See also

distance	returns the distance between two iterators (function template)
advance	advances an iterator by given distance (function template)
next	increment an iterator (function template)
prev	decrement an iterator (function template)
size	obtains the size of a range whose size can be calculated in constant time (customization point object)