std::copyable_function(3)

💖 NAME 💖

std::copyable_function - std::copyable_function

okay so bestie, this is the std::copyable_function(3) page from the C++ Standard Libary — yes, that’s how the manual spells it, and we’re keeping the lore 💅.

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✨ Synopsis ✨

Defined in header <functional>
template< class... >                                   (1) (since C++26)
class copyable_function; // not defined
template< class R, class... Args >

class copyable_function<R(Args...)>;
template< class R, class... Args >
class copyable_function<R(Args...) noexcept>;
template< class R, class... Args >
class copyable_function<R(Args...) &>;
template< class R, class... Args >
class copyable_function<R(Args...) & noexcept>;
template< class R, class... Args >
class copyable_function<R(Args...) &&>;
template< class R, class... Args >
class copyable_function<R(Args...) && noexcept>;       (2) (since C++26)
template< class R, class... Args >
class copyable_function<R(Args...) const>;
template< class R, class... Args >
class copyable_function<R(Args...) const noexcept>;
template< class R, class... Args >
class copyable_function<R(Args...) const &>;
template< class R, class... Args >
class copyable_function<R(Args...) const & noexcept>;
template< class R, class... Args >
class copyable_function<R(Args...) const &&>;
template< class R, class... Args >

class copyable_function<R(Args...) const && noexcept>;

okay so what even is it? The class template std::copyable_function is a general-purpose polymorphic function wrapper — and no cap, it’s giving main character energy for callables. std::copyable_function objects can store and invoke any CopyConstructible Callable target — functions, lambda expressions, bind expressions, or other function objects, as well as pointers to member functions and pointers to member objects. 🫶

The stored callable object is called the target of std::copyable_function. If a std::copyable_function contains no target, it is called empty. And this part is dramatic, bestie: unlike std::function, invoking an empty std::copyable_function results in undefined behavior. 😭 That is a “we don’t do that here” situation, fr fr.

std::copyable_functions supports every possible combination of cv-qualifiers, ref-qualifiers, and noexcept-specifiers not including volatile provided in its template parameter. These qualifiers and specifier (if any) are added to its operator(). ✨

std::copyable_function satisfies the requirements of CopyConstructible and CopyAssignable. 💖

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🎀 Member types 🎀

• result_type — R

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💅 Member functions 💅

• constructor (C++26) — constructs a new std::copyable_function object (public member function)
• destructor (C++26) — destroys a std::copyable_function object (public member function)
• operator= (C++26) — replaces or destroys the target (public member function)
• swap (C++26) — swaps the targets of two std::copyable_function objects (public member function)
• operator bool (C++26) — checks if the std::copyable_function has a target (public member function)
• operator() (C++26) — invokes the target (public member function)

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🫶 Non-member functions 🫶

• swap(std::copyable_function) (C++26) — overloads the std::swap algorithm (function)
• operator== (C++26) — compares a std::copyable_function with nullptr (function)

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📝 Notes 📝

Implementations may store a callable object of small size within the std::copyable_function object. Such small object optimization is effectively required for function pointers and std::reference_wrapper specializations, and can only be applied to types T for which std::is_nothrow_move_constructible_v<T> is true. 🧚

Feature-test macro           Value    Std      Feature
__cpp_lib_copyable_function  202306L  (C++26)  std::copyable_function

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🌸 Example 🌸

This section is incomplete Reason: example

the incomplete iconique energy is real 🙈

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👀 See also 👀

• function (C++11) — wraps callable object of any copy constructible type with specified function call signature (class template)
• move_only_function (C++23) — wraps callable object of any type with specified function call signature (class template)

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🏷️ Category 🏷️

• Todo with reason

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okay that’s the whole page, bestie 💖 signed off with love from http://cppreference.com, dated 2024.06.10 — mwah 🫶💋