On Wed, Aug 7, 2024 at 2:09 PM Victor Zverovich <victor.zverovich_at_[hidden]>
wrote:

> > We can't add a `formatter` specialization in one release and then remove
> it again in the next.
>
> it won't be removed. format_as doesn't replace a formatter specialization,
> just simplifies defining it for some use cases.
>

Oh yikes. Then either we should do a quick Zoom so I can figure out the
intent of P3070, or I should bring a competing proposal in the next mailing.
My impression had been that ADL `U format_as(T)` would be a replacement for
`std::formatter<T>` — it would allow a user-defined type `T` to be
formatted using the pre-existing `std::formatter<U>`, specifically so that
the user *would not need* to specialize `formatter<T>` for their own `T`.
For example, this would be a complete and working program:

#include <print>
namespace Mine {
  enum Color { RED, YELLOW };
  const char *format_as(Color c) { return (c == RED) ? "red" : "yellow"; }
}
int main() {
  std::print("{}\n", Mine::RED); // prints "red\n"
}

In fact this *seems* to be exactly how it works in {fmt}, so I guess I
don't understand what you're trying to say.
https://godbolt.org/z/esof9Ka76

–Arthur

>