Currently, operators do not support default arguments in most cases and must have a predetermined number of arguments.

For example, operator/ must have two arguments and those arguments cannot have defaults.  I propose allowing such operators to have additional arguments as long as they have defaults.  The default arguments must come after the regular arguments.

auto operator/(U, V) // OK
auto operator/(U, V, W) // Error, and should remain an error
auto operator/(U, V = V(), W) // Error, and should remain an error

auto operator/(U, V, W = W()) // Error, but should be ok

I don't think operator() would need to change at all as it already supports default arguments.  It would now need wording to allow defaults in any order.  Perhaps there are other operators with special cases that I haven't thought of.

The reason I want to have this feature is to use std::source_location with operators.  As far as I can tell, default arguments are the only sensible way to use std::source_location.

I think this is a backwards compatible change (but perhaps it could be detected by concepts? not 100% sure).

Feedback welcome.