Overload subscript operator in Fortran

I have some matrix type that can either be real or complex:

type t_mat
   logical :: is_real
   real    :: data_r(:,:)
   complex :: data_c(:,:)
end type

and I would like to overload the =-operator as well as the (i,j) operator, so that I could conveniently say:

type(t_mat) :: a

...

a(2,3) = 3

I know in C++ it is possible to overload the subscript operator. Does Fortran allow for something similar?