NAME¶

std::common_iterator::operator*,-> - std::common_iterator::operator*,->

Synopsis¶

constexpr decltype(auto) operator*(); (1) (since C++20)
constexpr decltype(auto) operator*() const (2) (since C++20)
requires /*dereferenceable*/<const I>;
constexpr auto operator->() const (3) (since C++20)
requires /* see description */;

Helper types¶

class /*proxy*/ {

std::iter_value_t<I> keep_;
constexpr proxy(std::iter_reference_t<I>&& x)
: keep_(std::move(x)) {}
public: (4) (exposition only*)
constexpr const std::iter_value_t<I>* operator->() const
noexcept {
return std::addressof(keep_);
}

};

Returns pointer or reference to the current element, or a proxy holding it.

The behavior is undefined if the underlying std::variant member object var does not
hold an object of type I, i.e. std::holds_alternative<I>(var) is equal to false.

Let it denote the iterator of type I held by var, that is std::get<I>(var).

1,2) Returns the result of dereferencing it.
3) Returns a pointer or underlying iterator to the current element, or a proxy
holding it:
* Equivalent to return it;, if I is a pointer type or if the expression
it.operator->() is well-formed.
* Otherwise, equivalent to auto&& tmp = *it; return std::addressof(tmp);, if
std::iter_reference_t<I> is a reference type.
* Otherwise, equivalent to return proxy(*it);, where proxy is an exposition only
class (4).
The expression in the requires-clause is equivalent to
std::indirectly_readable<const I> && (

requires(const I& i) { i.operator->(); } ||
std::is_reference_v<std::iter_reference_t<I>> ||
std::constructible_from<std::iter_value_t<I>, std::iter_reference_t<I>>

).

Parameters¶

(none)

Return value¶

1,2) Reference to the current element, or prvalue temporary. Equivalent to *it.
3) Pointer or iterator to the current element or proxy holding it as described
above.

Example¶

// Run this code

#include <complex>
#include <initializer_list>
#include <iostream>
#include <iterator>

using std::complex_literals::operator""i;

int main()
{
const auto il = {1i, 3.14 + 2i, 3i, 4i, 5i};

using CI = std::common_iterator<
std::counted_iterator<decltype(il)::iterator>,
std::default_sentinel_t>;

CI ci{std::counted_iterator{std::next(begin(il), 1), std::ssize(il) - 1}};

std::cout << *ci << ' ' << ci->real() << '\n';
}

Output:¶

(3.14,2) 3.14

Defect reports

The following behavior-changing defect reports were applied retroactively to
previously published C++ standards.

DR Applied to Behavior as published Correct behavior
LWG 3574 C++20 variant was fully constexpr (P2231R1) but also made constexpr
common_iterator was not
LWG 3595 C++20 functions of the proxy type lacked added
constexpr and noexcept
LWG 3672 C++20 operator-> might return by reference in always returns by
usual cases value

See also¶

constructor constructs a new iterator adaptor
(C++20) (public member function)