On 4 May 2025 21:38, Sebastian Wittmeier via Std-Proposals wrote:
> - it works without check. The exception just wanders to the next level.
> At the same time we can be noexcept. That is fine.

This defeats the purpose of noexcept. Noexcept specification is a
promise that the function won't throw. If you don't want that guarantee,
just don't mark it noexcept to begin with.

> -----Ursprüngliche Nachricht-----
> *Von:* Frederick Virchanza Gotham via Std-Proposals <std-
> proposals_at_[hidden]>
> *Gesendet:* So 04.05.2025 19:20
> *Betreff:* Re: [std-proposals] noexcept has gotten a bit hairy -- I
> want a compiler error
> *An:* std-proposals_at_[hidden];
> *CC:* Frederick Virchanza Gotham <cauldwell.thomas_at_[hidden]>;
> On Sat, May 3, 2025 at 7:10 PM Frederick Virchanza Gotham wrote:
> >
> > This is a very premature half-baked idea that popped into my head just
> > now . . .
>
>
> And I was also thinking that we should have a cast for adding or
> removing 'noexcept' from a function pointer, perhaps calling it
> 'noexcept_cast', and it should be constexpr.
>
> Presently here's how I'm doing it:
>
> #include <cstring>
>
> template<bool bFrom, typename T> struct NoExceptFromTrue {};
> template<bool bFrom, typename T> struct NoExceptFromFalse {};
>
> template<bool bTo, typename R, typename... Params>
> struct NoExceptFromTrue < bTo, R(*)(Params...) noexcept(true ) > {
> using type = R (*)(Params...) noexcept(bTo); };
> template<bool bTo, typename R, typename... Params>
> struct NoExceptFromFalse< bTo, R(*)(Params...) noexcept(false) > {
> using type = R (*)(Params...) noexcept(bTo); };
>
> template<bool bTo, typename R, typename Class, typename... Params>
> struct NoExceptFromTrue < bTo, R(Class::*)(Params...)
> noexcept(true ) > {
> using type = R (Class::*)(Params...) noexcept(bTo);
> };
>
> template<bool bTo, typename R, typename Class, typename... Params>
> struct NoExceptFromFalse< bTo, R(Class::*)(Params...)
> noexcept(false) > {
> using type = R (Class::*)(Params...) noexcept(bTo);
> };
>
> template<bool b, typename T>
> auto noexcept_cast(T const arg)
> {
> if constexpr ( requires { typename NoExceptFromTrue<b,
> T>::type(); } )
> {
> using Tto = typename NoExceptFromTrue<b, T>::type;
> return *static_cast<Tto const *>(static_cast<void
> const*>(&arg));
> }
> else
> {
> using Tto = typename NoExceptFromFalse<b, T>::type;
> return *static_cast<Tto const *>(static_cast<void
> const*>(&arg));
> }
> }
>
> int mystrlen1(char const *) { return 8; }
> int mystrlen2(char const *) noexcept { return 8; }
> int mystrlen3(char const *) noexcept(false) { return 8; }
>
> int main(int const arg, char **const argv)
> {
> auto func1 = noexcept_cast<true>( &mystrlen1 );
> auto func2 = noexcept_cast<true>( &mystrlen2 );
> auto func3 = noexcept_cast<true>( &mystrlen3 );
> auto func4 = noexcept_cast<true>( &std::strlen );
> return func1( argv[0] ) + func2( argv[0] ) + func3( argv[0] )
> + func4( argv[0] );
> }
>
> But I can't make it constexpr. Here's the GodBolt:
> https://godbolt.org/z/1b6qK6avo
>
> Maybe we should have either an operator, 'noexcept_cast', or a
> standard library function, 'std::noexcept_cast'.
> --
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>