_NOT_FN(3)

💅 _Not_fn< _Fn >(3) — Library Functions Manual

okay so bestie, sit down, because we're about to get into _Not_fn< _Fn >, and it is exactly what it sounds like: a Generalized negator. That's the whole vibe. It negates stuff. Generally. ✨

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🌸 NAME

_Not_fn< _Fn > — Generalized negator. That's it, that's the whole personality. 🎀

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✨ SYNOPSIS

🫶 Public Member Functions

• The big constructor — takes your callable and a sneaky int:

template<typename _Fn2 > constexpr _Not_fn (_Fn2 &&__fn, int)

• Move constructor — defaulted, so you don't gotta write it yourself, king:

_Not_fn (_Not_fn &&__fn)=default

• Copy constructor — also defaulted. Free real estate:

_Not_fn (const _Not_fn &__fn)=default

• operator() on an rvalue, but =deleted — it only exists when the thing is not invocable, which is the compiler's way of saying "nah bestie, this one's off the menu":

template<typename... _Args, typename  = enable_if_t<!__is_invocable<_Fn && , _Args...>::value>> void operator() (_Args &&... __args) &&=delete

• operator() on an lvalue, =deleted — same deal, !__is_invocable check, gone:

template<typename... _Args, typename  = enable_if_t<!__is_invocable<_Fn & , _Args...>::value>> void operator() (_Args &&... __args) &=delete

• operator() const &&, =deleted — deleted era 💀:

template<typename... _Args, typename  = enable_if_t<!__is_invocable<_Fn const && , _Args...>::value>> void operator() (_Args &&... __args) const &&=delete

• operator() const &, =deleted — last of the deleted squad, still const &:

template<typename... _Args, typename  = enable_if_t<!__is_invocable<_Fn const & , _Args...>::value>> void operator() (_Args &&... __args) const &=delete

🦋 Public Attributes

these next four are the ones that actually slay — they light up when __is_invocable is true, and they're all constexpr with noexcept specs that read like a whole paragraph. no cap, copy them character for character or the vibe check fails 🙈

• rvalue operator() — the && one, all constexpr'd up and noexcept-chain'd through _Fn &&:

template<typename... _Args, typename  = enable_if_t<__is_invocable<_Fn && , _Args...>::value>> constexpr decltype(_S_not< __inv_res_t< _Fn &&, _Args... >>()) operator() (_Args &&... __args) &&noexcept(__is_nothrow_invocable< _Fn &&, _Args... >::value &&noexcept(_S_not< __inv_res_t< _Fn &&, _Args... >>()))

• lvalue operator() — the & one, same energy but for _Fn &:

template<typename... _Args, typename  = enable_if_t<__is_invocable<_Fn & , _Args...>::value>> constexpr decltype(_S_not< __inv_res_t< _Fn &, _Args... >>()) operator() (_Args &&... __args) &noexcept(__is_nothrow_invocable< _Fn &, _Args... >::value &&noexcept(_S_not< __inv_res_t< _Fn &, _Args... >>()))

• const rvalue operator() — _Fn const && edition, iconic, no notes 👑

template<typename... _Args, typename  = enable_if_t<__is_invocable<_Fn const && , _Args...>::value>> constexpr decltype(_S_not< __inv_res_t< _Fn const &&, _Args... >>()) operator() (_Args &&... __args) const &&noexcept(__is_nothrow_invocable< _Fn const &&, _Args... >::value &&noexcept(_S_not< __inv_res_t< _Fn const &&, _Args... >>()))

• const lvalue operator() — _Fn const &, the final form, the main character 🌟:

template<typename... _Args, typename  = enable_if_t<__is_invocable<_Fn const & , _Args...>::value>> constexpr decltype(_S_not< __inv_res_t< _Fn const &, _Args... >>()) operator() (_Args &&... __args) const &noexcept(__is_nothrow_invocable< _Fn const &, _Args... >::value &&noexcept(_S_not< __inv_res_t< _Fn const &, _Args... >>()))

fr fr, every one of those signatures is constexpr, every one carries a noexcept(...) made of an __is_nothrow_invocable<...>::value and a noexcept(_S_not<...>()), and every enable_if_t gate is spelled out above exactly as it lives in the header. don't @ me, just copy it 💅

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🧚 Detailed Description

okay here's the actual declaration, and yes, the stray quote mark is canon, it's part of the lore:

template<typename _Fn>
    class _Not_fn< _Fn >" Generalized negator.

so yeah — template<typename _Fn>, class _Not_fn< _Fn >, and the whole bit is a Generalized negator. that's the sentence. that's the description. she's short, she's sweet, she's a template. obsessed. 💖

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🌈 Author

Generated automatically by Doxygen for libstdc++ from the source code. so nobody hand-wrote this one — it's a bot's magnum opus, and honestly? it ate. 🔥

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randomly thinking about how this page is libstdc++, dated Wed Oct 7 2026, and lives at _Not_fn< _Fn >(3) — anyway bestie, go negate something, you've got this 🫶💜