Fortran pointer as an argument to interface procedure
- by icarusthecow
Im trying to use interfaces to call different subroutines with different types, however, it doesnt seem to work when i use the pointer attribute. for example, take this sample code
MODULE ptr_types
TYPE, abstract :: parent
INTEGER :: q
END TYPE
TYPE, extends(parent) :: child
INTEGER :: m
END TYPE
INTERFACE ptr_interface
MODULE PROCEDURE do_something
END INTERFACE
CONTAINS
SUBROUTINE do_something(atype)
CLASS(parent), POINTER :: atype
! code determines that this allocation is correct from input
ALLOCATE(child::atype)
WRITE (*,*) atype%q
END SUBROUTINE
END MODULE
PROGRAM testpass
USE ptr_types
CLASS(child), POINTER :: ctype
CALL ptr_interface(ctype)
END PROGRAM
This gives error
Error: There is no specific subroutine for the generic 'ptr_interface' at (1)
however if i remove the pointer attribute in the subroutine it compiles fine. Now, normally this wouldnt be a problem, but for my use case i need to be able to treat that argument as a pointer, mainly so i can allocate it if necessary.
Any suggestions? Mind you I'm new to fortran so I may have missed something
edit: forgot to put the allocation in the parents subroutine, the initial input is unallocated
EDIT 2
this is my second attempt, with caller side casting
MODULE ptr_types
TYPE, abstract :: parent
INTEGER :: q
END TYPE
TYPE, extends(parent) :: child
INTEGER :: m
END TYPE
TYPE, extends(parent) :: second
INTEGER :: meow
END TYPE
CONTAINS
SUBROUTINE do_something(this, type_num)
CLASS(parent), POINTER :: this
INTEGER type_num
IF (type_num == 0) THEN
ALLOCATE (child::this)
ELSE IF (type_num == 1) THEN
ALLOCATE (second::this)
ENDIF
END SUBROUTINE
END MODULE
PROGRAM testpass
USE ptr_types
CLASS(child), POINTER :: ctype
SELECT TYPE(ctype)
CLASS is (parent)
CALL do_something(ctype, 0)
END SELECT
WRITE (*,*) ctype%q
END PROGRAM
however this still fails. in the select statement it complains that parent must extend child. Im sure this is due to restrictions when dealing with the pointer attribute, for type safety, however, im looking for a way to convert a pointer into its parent type for generic allocation. Rather than have to write separate allocation functions for every type and hope they dont collide in an interface or something.
hopefully this example will illustrate a little more clearly what im trying to achieve, if you know a better way let me know
