std::experi...::operator=(3)

okay bestie, this is the C++ Standard Libary manual page for std::experimental::optional::operator= — manual name: std::experi...::operator=(3). Yes, it's giving assignment energy, and we're gonna make it make sense. 💅

🌸 NAME 🌸

std::experimental::optional::operator= — std::experimental::optional::operator=

✨ Synopsis ✨

optional& operator=( std::experimental::nullopt_t )    (1) (library
fundamentals TS)
noexcept;
optional& operator=( const optional& other );          (2) (library
fundamentals TS)
optional& operator=( optional&& other ) noexcept(/*    (3) (library
fundamentals TS)
see below */);
template< class U >                                    (4) (library
fundamentals TS)
optional& operator=( U&& value );

Replaces contents of *this with the contents of other.

1) If *this contains a value before the call, the contained value is destroyed by calling its destructor as if by val->T::~T(). *this does not contain a value after this call.

2,3) Assigns the state of other. The way this plays out:

• If both *this and other do not contain a value, the function has no effect.
• If *this contains a value, but other does not, then the contained value is destroyed by calling its destructor. *this does not contain a value after the call.
• If other contains a value, then depending on whether *this contains a value, the contained value is either direct-initialized or assigned from *other (2) or std::move(*other) (3). Note that a moved-from optional still contains a value.

4) Decay-only perfect-forwarded assignment: depending on whether *this contains a value before the call, the contained value is either direct-initialized from std::forward<U>(value) or assigned from std::forward<U>(value). The function does not participate in overload resolution unless std::is_same<std::decay_t<U>, T>::value is true.

💖 Parameters 💖

• other — another optional object whose contained value to assign
• value — value to assign to the contained value

🎀 Type requirements 🎀

• T must meet the requirements of CopyAssignable and CopyConstructible in order to use overload (2).
• T must meet the requirements of MoveAssignable and MoveConstructible in order to use overload (3).

🫶 Return value 🫶

*this

😭 Exceptions 😭

2-4) Throws any exception thrown by the constructor or assignment operator of T. If an exception is thrown, the initialization state of *this (and of other in case of (2)) is unchanged, i.e. if the object contained a value, it still contains a value, and the other way round. The contents of value and the contained values of *this and other depend on the exception safety guarantees of the operation from which the exception originates (copy-constructor, move-assignment, etc.).

(3) has the following noexcept declaration:

noexcept specification:
noexcept(std::is_nothrow_move_assignable<T>::value &&
std::is_nothrow_move_constructible<T>::value)

🦋 Notes 🦋

An optional object op may be turned into an empty optional with both op = {}; and op = nullopt;.

🌈 Example 🌈

// Run this code

#include <experimental/optional>
#include <iostream>

int main()
{
    std::experimental::optional<const char*> s1 = "abc", s2; // constructor
    s2 = s1; // assignment
    s1 = "def"; // decaying assignment (U = char[4], T = const char*)
    std::cout << *s2 << ' ' << *s1 << '\n';
}

Output:

abc def

👑 See also 👑

• emplace — constructs the contained value in-place (public member function)

🏷️ Categories 🏷️

• Noindexed pages
• conditionally noexcept

that's the whole page, bestie 💖 source: http://cppreference.com · version/date: 2024.06.10 · page: std::experi...::operator=(3) — byeee 🫶