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

💅 std::move_only_function::operator= 💅

okay so bestie, welcome to page std::move_o...::operator=(3) from the C++ Standard Library man pages — yes, the title's abbreviated like that, we don't make the rules 💀. This is the assignment operator for std::move_only_function, and it's lowkey giving "assign a new target or yeet the old one" energy. Let's get into it 🫶

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✨ NAME ✨

std::move_only_function::operator= — literally std::move_only_function::operator=, no cap 💅

🌸 Synopsis 🌸

Here's the whole roster, bestie — four overloads, all since C++23:

move_only_function& operator=( move_only_function&& other );

(1) (since C++23)

move_only_function& operator=( const move_only_function& ) = delete;

(2) (since C++23)

move_only_function& operator=( std::nullptr_t ) noexcept;

(3) (since C++23)

template< class F >

(4) (since C++23)

move_only_function& operator=( F&& f );

So what does it actually do? It assigns a new target to std::move_only_function or destroys its target. That's the whole vibe check. Now let's break down each overload, because the details matter and we are not skipping them 😤

1. Moves the target of other to *this, or destroys the target of *this (if any) if other is empty, by auto(std::move(other)).swap(*this). After move assignment, other is in a valid state with an unspecified value — so she's alive but her exact contents are a mystery, iconic behavior honestly 🙈
2. The copy assignment operator is deleted. std::move_only_function does not satisfy CopyAssignable. Not me getting blocked from copying, it's giving move-only main character energy 💀
3. Destroys the current target if it exists. After the call, *this is empty. Clean slate, no notes ✨
4. Sets the target of *this to the callable f, or destroys the current target if f is a null function pointer, a null pointer to member function, or an empty std::move_only_function, as if by executing move_only_function(std::forward<F>(f)).swap(*this);. This overload participates in overload resolution only if the constructor of move_only_function from F participates in overload resolution. And heads up: the program is ill-formed or has undefined behavior if the selected constructor call is ill-formed or has undefined behavior — so like, pay attention bestie 😭

🎀 Parameters 🎀

• other — another std::move_only_function object to move the target of.
• f — a callable object to initialize the new target with.

💖 Return value 💖

*this — that's it, that's the return value. periodt 💅

🦋 Notes 🦋

It is intentional not to require the move assignment operator to be noexcept to leave room for an allocator-aware move_only_function in future. So don't come for her about the missing noexcept, it's a whole future-proofing thing 🌈

Also: move_only_function can be assigned from std::in_place_type<Fn> given it can be constructed from that argument. cute, flexible, obsessed 🎀

👑 See also 👑

• operator= assigns a new target (public member function of std::function<R(Args...)>)

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and that's the page, bestie 🫶 source is http://cppreference.com, version 2024.06.10, and the footer name is std::move_o...::operator=(3) — go forth and assign your targets responsibly 💜✨