Polymorphisms of Parameterized Derived Extension Types Are Not Recommended

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