Would it be affected by the design decision of retiring niebloids? P3136 https://github.com/cplusplus/papers/issues/1790   -----Ursprüngliche Nachricht----- Von:Avi Kivity via Std-Proposals <std-proposals_at_[hidden]> Gesendet:So 01.12.2024 19:43 Betreff:Re: [std-proposals] std::construct<T> An:Andrey Semashev <andrey.semashev_at_[hidden]>; std-proposals_at_[hidden]; CC:Avi Kivity <avi_at_[hidden]>; On Sun, 2024-12-01 at 21:25 +0300, Andrey Semashev wrote: > On December 1, 2024 7:57:45 PM Avi Kivity <avi_at_[hidden]> wrote: > > > On Sun, 2024-12-01 at 19:11 +0300, Andrey Semashev via Std- > > Proposals > > wrote: > > > On December 1, 2024 6:57:16 PM Avi Kivity via Std-Proposals > > > <std-proposals_at_[hidden]> wrote: > > > > > > > Functions and member functions are invocable, but constructors > > > > are > > > > not. > > > > > > > > I propose to add > > > > > > > > template <typename T, typename... Args> > > > > T std::construct(Args&&... args) { > > > >   return T(std::forward<decltype(Args)>(args)...); > > > > } > > > > > > > > With this, we can pass a constructor where other functions can > > > > be > > > > passed. > > > > > > > >   // build a callback that creates and returns a Type1 thing > > > >   std::function<Type1 (Arg3)> make_somthing = > > > > std::bind_front(std::construct<Type1>, arg1, std::ref(arg2)); > > > > > > > >   // transform a vector of ints to a vector of some other type > > > >   auto foo = some_container | > > > > std::views::transform(std::construct<AnotherType>) | > > > > std::ranges::to<std::vector>(); > > > > > > Binding a function pointer is less efficient than a function > > > object. > > > > Typically, inlining will remove the difference. > > The function pointer must still increase the size of the binder, > which may > make it too large to fit in e. g. std::function small buffer. > > And whether the compiler is able to devirtualize the call is more of > a > question than with a function object with an inline operator(). > > > Or we can make it a > > niebloid. > > Sorry, I don't know what this means. > A technique used in std::ranges to avoid such pointers-to-functions. template <typename T> struct _Impl_construct     template <typename... Args>     static T operator()(Args... args) { return T(std::forward<Args>(args)...); } }; template <typename T> inline _Impl_construct construct; > > > > > > > And > > > given that lambdas are an easy way to create function objects, I > > > don't > > > really see the benefits of the proposal. > > > > > > I believe that writing > > > >    std::views::transform(std::construct<AnotherType>) > > > > is more readable than > > > >    std::views::transform([] (auto&& x) { return > > AnotherType<std::forward<decltype(x)>(x); }); > > I think this is not equivalent to the original example. Is > AnotherType a > template? > I mistyped, sorry. std::views::transform([] (auto&& x) { return AnotherType(std::forward<decltype(x)>(x)); }); The intent is to construct an object of type AnotherType using a single parameter of unknown type. -- Std-Proposals mailing list Std-Proposals_at_[hidden] https://lists.isocpp.org/mailman/listinfo.cgi/std-proposals