So we would need new syntax, which creates exceptions to the conversion rules to make a workaround work in more cases by artificially widening, where and when elision is done and propagating the usage of this feature through function call hierarchies. Even if you have identified a missing piece, where C++ can be more complete, powerful and performant, the solution seems too complicated by a lot. For the same price (syntax, amount of rules, teaching) one can probably extend C++ with a broad feature that is less an exception to the rules, but now naturally expand on them and has broader usage.


 

-----Ursprüngliche Nachricht-----
Von: Frederick Virchanza Gotham via Std-Proposals <std-proposals@lists.isocpp.org>
Gesendet: Di 12.09.2023 01:36
Betreff: Re: [std-proposals] Copy-construct, move-construct, and PR-construct
An: std-proposals@lists.isocpp.org;
CC: Frederick Virchanza Gotham <cauldwell.thomas@gmail.com>;
On Sun, Sep 10, 2023 at 2:20 PM Frederick Virchanza Gotham wrote:
>
> If we were to instead mark the class, for example:


So we already looked at two possibilities:
(1) Mark the conversion operator
(2) Mark the class

The third possibility would be to have a base class that favours conversion:

   class Monkey : public std::priority_conversion< std::mutex > {
   public:
       operator std::mutex(void)
       {
           // return a mutex from in here
       }
   };

And so when the compiler encounters the invocation of a constructor
with just one argument, it checks to see if the argument is of a class
type that inherits from "std::priority_conversion", and if it does, it
invokes the conversion before passing the sole argument to the
constructor.
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