Manual Reference Pages - same_type_as (3fortran)

NAME

SAME_TYPE_AS(3) - [STATE:INQUIRY] Query dynamic types for equality

SYNOPSIS

result = same_type_as(a, b)

         logical same_type_as(a, b)

          type(TYPE(kind=KIND)),intent(in) :: a
          type(TYPE(kind=KIND)),intent(in) :: b

CHARACTERISTICS

o A shall be an object of extensible declared type or unlimited polymorphic. If it is a polymorphic pointer, it shall not have an undefined association status.

o B shall be an object of extensible declared type or unlimited polymorphic. If it is a polymorphic pointer, it shall not have an undefined association status.

DESCRIPTION

SAME_TYPE_AS(3) queries the dynamic types of objects for equality.

OPTIONS

o A : object to compare to B for equality of type

o B : object to be compared to for equality of type

RESULT

If the dynamic type of A or B is extensible, the result is true if and only if the dynamic type of A is the same as the dynamic type of B. If neither A nor B has extensible dynamic type, the result is processor dependent.

NOTE1

The dynamic type of a disassociated pointer or unallocated allocatable variable is its declared type. An unlimited polymorphic entity has no declared type.

NOTE2

The test performed by SAME_TYPE_AS is not the same as the test performed by the type guard TYPE IS. The test performed by SAME_TYPE_AS does not consider kind type parameters.

Sample program:

      ! program demo_same_type_as
      module M_ether
      implicit none
      private

      type   :: dot
        real :: x=0
        real :: y=0
      end type dot

      type, extends(dot) :: point
        real :: z=0
      end type point

      type something_else
      end type something_else

      public :: dot
      public :: point
      public :: something_else

      end module M_ether

      program demo_same_type_as
      use M_ether, only : dot, point, something_else
      implicit none
      type(dot) :: dad, mom
      type(point) :: me
      type(something_else) :: alien

       write(*,*)same_type_as(me,dad),’I am descended from Dad, but equal?’
       write(*,*)same_type_as(me,me) ,’I am what I am’
       write(*,*)same_type_as(dad,mom) ,’what a pair!’

       write(*,*)same_type_as(dad,me),’no paradox here’
       write(*,*)same_type_as(dad,alien),’no relation’

       call pointers()
       contains
       subroutine pointers()
       ! Given the declarations and assignments
       type t1
          real c
       end type
       type, extends(t1) :: t2
       end type
       class(t1), pointer :: p, q, r
          allocate (p, q)
          allocate (t2 :: r)
          ! the result of SAME_TYPE_AS (P, Q) will be true, and the result
          ! of SAME_TYPE_AS (P, R) will be false.
          write(*,*)’(P,Q)’,same_type_as(p,q),"mind your P’s and Q’s"
          write(*,*)’(P,R)’,same_type_as(p,r)
       end subroutine pointers

      end program demo_same_type_as

Results:

F I am descended from Dad, but equal? T I am what I am T what a pair! F no paradox here F no relation (P,Q) T mind your P’s and Q’s (P,R) F

STANDARD

Fortran 2003

o	A shall be an object of extensible declared type or unlimited polymorphic. If it is a polymorphic pointer, it shall not have an undefined association status.
o	B shall be an object of extensible declared type or unlimited polymorphic. If it is a polymorphic pointer, it shall not have an undefined association status.

o	A : object to compare to B for equality of type
o	B : object to be compared to for equality of type