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

< cpp‎ | utility‎ | expected
Utilities library
Language support
Type support (basic types, RTTI)
Library feature-test macros (C++20)
Dynamic memory management
Program utilities
Coroutine support (C++20)
Variadic functions
Debugging support
Three-way comparison
General utilities
Date and time
Function objects
Formatting library (C++20)
Relational operators (deprecated in C++20)
Integer comparison functions
Swap and type operations
Common vocabulary types
Elementary string conversions

Primary template
constexpr const T* operator->() const noexcept;
(1) (since C++23)
constexpr T* operator->() noexcept;
(2) (since C++23)
constexpr const T& operator*() const& noexcept;
(3) (since C++23)
constexpr T& operator*() & noexcept;
(4) (since C++23)
constexpr const T&& operator*() const&& noexcept;
(5) (since C++23)
constexpr T&& operator*() && noexcept;
(6) (since C++23)
void partial specialization
constexpr void operator*() const noexcept;
(7) (since C++23)

Accesses the expected value contained in *this.

1,2) Returns a pointer to the expected value.
3-6) Returns a reference to the expected value.
7) Returns nothing.

If has_value() is false, the behavior is undefined.


[edit] Return value

3,4) val
5,6) std::move(val)

[edit] Notes

These operators do not check whether the optional represents an expected 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 = "error"s; // error, ex1 contains an expected value of type int
    ex1 = std::unexpected("error"s);
    // *ex1 = 13; // UB, ex1 contains an 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 expected value by calling operator* on an std::expected rvalue
    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]