I understand what you are saying. I wonder/doubt if the comma would have to be an explicit step as part of the hand over to the std lib. The comma is a separa

I understand what you are saying. I wonder/doubt if the comma would have to be an explicit step as part of the hand over to the std lib. The comma is a separator that the programmer would use, but does the compiler need that? The compiler needs to translate 1 argument to multiple arguments of multiple types, such that stdlib can receive all info. (The original fstring indeed cannot be expanded by the lib itself, since that would give stdlib a special status). So the needed language feature is a one to multi args translation, where at compile time all types are known. That would mean that in the context of an assignment (in stead of a function argument), the f string does not make sense. In that case the compilation can simply fail, no? I guess the handing over the multiple args of different types is a problem. Not all infinite combinations can be solved by templating and I guess even if it could, the header would contain too much logic since the template expansion needs to happen from the header?