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std::common_iterator<I,S>::common_iterator

constexpr common_iterator() requires std::default_initializable<I> = default;
 (1) (since C++20) 
constexpr common_iterator( I i );
 (2) (since C++20) 
constexpr common_iterator( S s );
 (3) (since C++20) 
template< class I2, class S2 >
requires std::convertible_to<const I2&, I> && 
         std::convertible_to<const S2&, S>
constexpr common_iterator( const common_iterator<I2, S2>& x );
 (4) (since C++20)

Constructs a new iterator adaptor, effectively initializes the underlying std::variant<I, S> member object var to hold an I (iterator) or S (sentinel) object.

1) Default constructor. Default-initializes var. After construction, var holds a value-initialized I object. Operations on the resulting iterator adaptor have defined behavior if and only if the corresponding operations on a value-initialized I also have defined behavior.
2) After construction, var holds an I object move-constructed from i.
3) After construction, var holds an S object move-constructed from s.
4) After construction, var holds an I or S object initialized from the I2 or S2 held by x.var, if x.var holds that alternative, respectively. The behavior is undefined if x is in an invalid state, that is, x.var.valueless_by_exception() is equal to true.

Parameters

i - iterator to adapt
s - sentinel to adapt
x - iterator adaptor to copy

Example

#include <algorithm>
#include <iostream>
#include <iterator>
#include <numeric>
#include <vector>
 
int main()
{
    std::vector v{3, 1, 4, 1, 5, 9, 2};
 
    using CI = std::common_iterator<
                   std::counted_iterator<std::vector<int>::iterator>,
                   std::default_sentinel_t>;
    CI unused; // (1)
    CI start{std::counted_iterator{std::next(begin(v)), ssize(v) - 2}}; // (2)
    CI finish{std::default_sentinel}; // (3)
    CI first{start}; // (4)
    CI last{finish}; // (4)
 
    std::copy(first, last, std::ostream_iterator<int>{std::cout, " "});
    std::cout << '\n';
 
    std::common_iterator<
        std::counted_iterator<
            std::ostream_iterator<double>>,
            std::default_sentinel_t>
            beg{std::counted_iterator{std::ostream_iterator<double>{std::cout,";  "}, 5}},
            end{std::default_sentinel};
    std::iota(beg, end, 3.1);
    std::cout << '\n';
}

Output:

1 4 1 5 9
3.1;  4.1;  5.1;  6.1;  7.1;

See also

(C++20)
assigns another iterator adaptor
(public member function)

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