module generics Type T contains procedure :: A procedure :: B generic :: C=>A, B end type T contains subroutine A(X,Y,Z) class(T) X real Y real, optional :: Z end subroutine subroutine B(X,Y,Z) class(T) X class(*), optional :: Y, Z end subroutine end module generics
The two subroutines are ambiguous (e.g. for C%(x,1.,2.)). But ifort accepts this when you compile the module, rejecting it only if you try to use it in any way that is ambiugous. gfortran rejects it as soon as you compile the module. So when is non-ambiguity required? The standard doesn't seem to be very obviously clear on this.
For libraries it would be useful to have at least some compile-time warning that there may be ambiguous call cases.