# std::common_iterator<I,S>::operator*,->

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< cpp‎ | iterator‎ | common iterator

constexpr decltype(auto) operator*(); | (1) | (since C++20)
constexpr decltype(auto) operator*() const requires /*dereferenceable*/<const I>; | (2) | (since C++20)
constexpr auto operator->() const requires /* see description */; | (3) | (since C++20)
Helper types |  |
class /*proxy*/ { std::iter_value_t<I> keep_; constexpr proxy(std::iter_reference_t<I>&& x) : keep_(std::move(x)) {} public: constexpr const std::iter_value_t<I>* operator->() const noexcept { return std::addressof(keep_); } }; | (4) | (exposition only*)

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 <algorithm>
    #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 `common_iterator` was not | also made constexpr
LWG 3595 | C++20 | functions of the proxy type lacked constexpr and noexcept | added
LWG 3672 | C++20 | `operator->` might return by reference in usual cases | always returns by value

### See also

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

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