- A function/subroutine is
generic
if the function/subroutine name
can be
associated with a more than one
function/subroutine
The number and the type of parameters in the function/subroutine invocation will determine actual subroutine/function that will be invoked.
(In C++ parlons, a generic function/subroutine is an overloaded function
- (The above was explained using F90 lingo)
- Recall that the
interface block
can contain
function declaration
- There is
another use
for
interface block :
- The interface block can be used to define generic functions/subroutines
- Example:
INTERFACE this_or_that SUBROUTINE this(x) integer :: x END SUBROUTINE SUBROUTINE that(x) real :: x END SUBROUTINE END INTERFACE
- Effect of a "named" interface
- When the F90 compiler translates a function/subroutine name that matches the name of an interface , it replaces the invocation with one of the function/subroutine in the interface depending on the number and type of parameters
Example:
PROGRAM main IMPLICIT NONE INTERFACE my_function SUBROUTINE f1(x) ! integer integer :: x END SUBROUTINE SUBROUTINE f2(x) ! real real :: x END SUBROUTINE SUBROUTINE f3(x, y) ! integer, real integer :: x real :: y END SUBROUTINE END INTERFACE INTEGER i REAL r CALL my_function(i) CALL my_function(r) CALL my_function(i,r) END
- Example Program:
(Demo above code)
- Prog file: click here
- Do these:
- Compile with:
f90 -S generic-func01.f90
- Look at the compile code, search for the string, you will see:
! 22 CALL my_function(i) ... call f1_ ! 23 CALL my_function(r) ... call f2_ ! 24 CALL my_function(i,r) ... call f3_
- Compile with:
f90 -S generic-func01.f90
- F90 can
pass parameters
in two ways:
- Implicitly :
the parameter
and
the value
are matched up by
ranking (ordering)
- Explicitly : the parameter and the value are matched up by name
- Implicitly :
the parameter
and
the value
are matched up by
ranking (ordering)
- Example:
INTERFACE SUBROUTINE f3(x, y) integer :: x real :: y END SUBROUTINE END INTERFACE INTEGER :: i = 1 REAL :: r = 3.14 CALL f3(i,r) ! Implicit, with correct order OK CALL f3(x=i,y=r) ! Explicit, with correct order OK CALL f3(y=r,x=i) ! Explicit, with wrong order, still OK !!! CALL f3(r,i) ! Implicit, with wrong order, Not OK...
- Example Program:
(Demo above code)
- Prog file: click here
- Consequence of the explicit parameter passing feature:
- A poor choice of parameter names can make two functions indistinguishable (and cause F90 to report ambiguity
- Example:
INTERFACE my_function SUBROUTINE f1(x, y) ! <--- my_function(x=i, y=r) integer :: x real :: y END SUBROUTINE SUBROUTINE f2(y, x) ! <--- my_function(x=i, y=r) real :: y integer :: x END SUBROUTINE END INTERFACEThere is ambiguity because the call
INTEGER i REAL r CALL my_function( x=i, y=r )
can invoke either f1() or f2() !!
- Example Program:
(Demo above code)
- Prog file: click here
- NOTE:
- Try changing the name of one parameter - the ambiguity problem will go away