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

From cppreference.com
< cpp‎ | utility‎ | expected
 
 
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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.

Contents

[edit] Parameters

(none)

[edit] Return value

Pointer or reference to the contained value.

[edit] 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.

[edit] 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

[edit] See also

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