Association

Association allows different program units to access the same value through different names. Entities are associated when each is associated with the same storage location.

There are four kinds of association:

The following example shows name, pointer, and storage association between an external program unit and an external procedure.

Example of Name, Pointer, and Storage Association


! Scoping Unit 1: An external program unit

REAL A, B(4)
REAL, POINTER :: M(:)
REAL, TARGET :: N(12)
COMMON /COM/...
EQUIVALENCE (A, B(1))        ! Storage association between A and B(1)
M => N                       ! Pointer association
CALL P (actual-arg,...)
...
 
! Scoping Unit 2: An external procedure
SUBROUTINE P (dummy-arg,...)  ! Name and storage association between         
                              !    these arguments and the calling                     
                              !    routine's arguments in scoping unit 1
  COMMON /COM/...             ! Storage association with common block COM
                              !    in scoping unit 1

  REAL Y
  CALL Q (actual-arg,...)
  CONTAINS
    SUBROUTINE Q (dummy-arg,...) ! Name and storage association between                                 
                                 !   these arguments and the calling
                                 !   routine's arguments in host procedure        
                                 !   P (subprogram Q has host association               
                                 !   with procedure P)
      Y = 2.0*(Y-1.0)       ! Name association with Y in host procedure P
    ...

The following example shows inheritance association:


TYPE POINT                  ! A base type
REAL :: X, Y
END TYPE POINT 

TYPE, EXTENDS(POINT) :: COLOR_POINT   ! An extension of TYPE(POINT)
                                      ! Components X and Y, and component name POINT,
                                      !   are inherited from the parent type POINT
INTEGER :: COLOR
END TYPE COLOR_POINT