std::expected<T,E>::operator->, std::expected<T,E>::operator*
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Common vocabulary types
std::expected
expected::operator->expected::operator*
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.
(until C++26)If has_value() is false:
- If the implementation is hardened, a contract violation occurs. Moreover, if the contract-violation handler returns under "observe" evaluation semantic, the behavior is undefined.
- If the implementation is not hardened, the behavior is undefined.
Contents
[edit] Return value
1,2) std::addressof (
val )3,4)
val [edit] Notes
These operators do not check whether the optional represents an expected value, users can do so manually by using has_value() or operator bool(). Alternatively, if checked access is needed, value() or value_or() may be used.
[edit] Example
Run this code
#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