24 Ranges library [ranges]

24.7 Range adaptors [range.adaptors]

24.7.13 Common view [range.common]

24.7.13.1 Overview [range.common.overview]

1
#
common_­view takes a view which has different types for its iterator and sentinel and turns it into a view of the same elements with an iterator and sentinel of the same type.
2
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[ Note
:
common_­view is useful for calling legacy algorithms that expect a range's iterator and sentinel types to be the same.
— end note
 ]
3
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The name views​::​common denotes a range adaptor object ([range.adaptor.object]).
Given a subexpression E, the expression views​::​common(E) is expression-equivalent to:
  • (3.1)
    views​::​all(E), if decltype((E)) models common_­range and views​::​all(E) is a well-formed expression.
  • (3.2)
    Otherwise, common_­view{E}.
4
#
[ Example
: 
// Legacy algorithm:
template<class ForwardIterator>
size_t count(ForwardIterator first, ForwardIterator last);

template<forward_range R>
void my_algo(R&& r) {
  auto&& common = common_view{r};
  auto cnt = count(common.begin(), common.end());
  // ...
}
— end example
 ]