std::expected<T,E>::operator->, std::expected<T,E>::operator*

T is not cv void 
constexpr const T* operator->() const noexcept;
 (1) (since C++23) 
constexpr T* operator->() noexcept;
 (1) (since C++23) 
constexpr const T& operator*() const& noexcept;
 (2) (since C++23) 
constexpr T& operator*() & noexcept;
 (2) (since C++23) 
constexpr const T&& operator*() const&& noexcept;
 (2) (since C++23) 
constexpr T&& operator*() && noexcept;
 (2) (since C++23)
T is cv void 
constexpr void operator*() const noexcept;
 (3) (since C++23)

Accesses the expected value contained in *this.

1) Returns a pointer to the contained value.
2) Returns a reference to the contained value.
3) Returns nothing.

The behavior is undefined if this->has_value() is false.

Parameters

(none)

Return value

Pointer or reference to the contained value.

Notes

These operators do not check whether the optional contains a value! You can do so manually by using has_value() or simply operator bool(). Alternatively, if checked access is needed, value() or value_or() may be used.

Example

#include <cassert>
#include <expected>
#include <iomanip>
#include <iostream>
#include <string>
 
int main()
{
    using namespace std::string_literals;
 
    std::expected<int, std::string> ex1 = 6;
    assert(*ex1 == 6);
 
    *ex1 = 9;
    assert(*ex1 == 9);
 
    ex1 = std::unexpected("error"s);
    // *ex1 = 13 // UB, ex1 contains "unexpected" value
    assert(ex1.value_or(42) == 42);
 
    std::expected<std::string, bool> ex2 = "Moon"s;
    std::cout << "ex2: " << std::quoted(*ex2) << ", size: " << ex2->size() << '\n';
 
    // You can "take" the contained value by calling operator* on an rvalue to expected
 
    auto taken = *std::move(ex2);
    std::cout << "taken: " << std::quoted(taken) << "\n"
                 "ex2: " << std::quoted(*ex2) << ", size: " << ex2->size() << '\n';
}

Possible output:

ex2: "Moon", size: 4
taken: "Moon"
ex2: "", size: 0

See also

returns the expected value
(public member function)
returns the expected value if present, another value otherwise
(public member function)
checks whether the object contains an expected value
(public member function)
returns the unexpected value
(public member function)

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