What should noexcept_cast do, if an exception is thrown? Should if have code to catch?    - No code to catch, that is the point. UB!  - Code to catch for each call, and terminate. Safer.  - Neither. Compile error, if actual noexcept cannot be proven by the compiler. No guarantee that valid programs compile, however.   -----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'. -- Std-Proposals mailing list Std-Proposals_at_[hidden] https://lists.isocpp.org/mailman/listinfo.cgi/std-proposals