Polymorphisms of Parameterized Derived Extension Types Are Not Recommended

Polymorphisms of parameterized derived extension types are not recommended. They may cause problems in some cases.

For example:

module test
  implicit none
  type :: ty(a, b)
    integer, len :: a, b
    real(4) :: r1(b)
  end type
  type, extends (ty) :: ty1(c)
    Integer, len :: c
    real(4) :: r2(c)
  end type
end module
 
program main
  use test
  implicit none
  type (ty1(:, :, :)), allocatable :: x
  allocate (ty1(3, 2, 20) :: x)
  x%r1 = 1.0
  x%r2 = 2.0
end program