J3/04-217

Date:     2004-01-14
To:       J3
From:     Walt Brainerd
Subject:  Alternate addressing of structure components

Date:
2004-01-08 at 08:14:09

Request number:
Pub-110

Name:
Jack Saba

E_mail:
jack.saba@gsfc.nasa.gov

==========================================================
Number:

Title: Alternate addressing of structure components

Submitted by: J3

Status: For Consideration

References:

Basic Functionality: Ability to access components of structures using location
of component in the structure (or some other method compatible
with accessing via loop).


Rationale: There are instances (many, in my case) where one wants to do
the same thing to all components of a structure. In Fortran
95, it is necessary to rewrite essentially the same code
(even if it is only a call to a subroutine) separately for
each component. With this feature, it would be possible to
access all components using a do loop. For example, if the
syntax chosen was to use the component location in the
structure enclosed in parentheses, one could write

DO i=1,N
   CALL DoSomethingWithComponents ( Struct % (i) )
END DO

rather than having a list of (sometimes many) calls, one
for each component.

Estimated Impact: I don't know how easy this would be to implement.

The Interactive Data Language (IDL) has such a feature. Its
presence there has made a marked difference on code
complexity and hence the time it takes to write, debug, and
maintain the code. I have written some code in IDL rather
than Fortran specifically because of this feature.

Detailed Specification: Probably not in the appropriate format, since I'm not sure
what that is, but...

Structure components shall be accessible by using their
locations within the structure. The syntax for this shall
be the location enclosed within parentheses, in place of the
component name.

Example: Struct % SecondComponent and Struct % (2) will both
access the same compoent of the structure Struct.

History: Submitted as Pub-110