As in the title.

Reason: currently I have an asynchronous logger. If one call the macro

LOG("{a} {b}", "a"_a=x, "b"_a=y);

I'd like to be able to

1. compute x1 = TransformOnCallingThread(x); y1 = TransformOnCallingThread(y);
2. send the format string, x1 and y1 to the logging thread with an inter-thread queue
3. call fmt::format("{a} {b}", "a"_a=x1, "b"_a=y1)

Currently, as far as I can see, (1) requires reaching into the fmt::detail namespace.