VHDL Issue Number:      0015
Classification:         Language Definition Problem
Language Version:       VHDL-87
Summary:                Bounds and direction of certain unconstrained
                        formals are undefined
Related Issues:
Relevant LRM Sections:  3.2.1.1
Key Words and Phrases:  Unconstrained formals, subelement association
Current Status:         ISAC-Approved
1076-1993 Disposition:  Closed (All Issues Completely Addressed)
Disposition Rationale:  LRM is clear now.
Superseded By:          N/A
-----------------------
Date Submitted:         1989/02/10
Author of Submission:   Doug Dunlop
Author's Affiliation:   Intermetrics, Inc.
Author's Post Address:  4733 Bethesda Ave #415
                        Bethesda, MD  20814
Author's Phone Number:  (301) 657-3775
Author's Fax Number:    
Author's Net Address:   dunlop@inmet.inmet.com
-----------------------
Date Analyzed:          1991/01/15
Author of Analysis:     Chuck Swart
Revision Number:        $Revision: 1.10 $
Date Last Revised:      $Date: 1995/05/13 19:34:42 $


Description of Problem
----------------------
LRM 3.2.1.1 defines the index range of an unconstrained formal to be taken from
the "corresponding association element".  This definition is not applicable if
the subelements of the formal are associated on an individual basis.  At one
time it was the intent of CLSI to disallow subelement associations for an
unconstrained formal.  It is probably an oversight that this is not disallowed.


Proposed Resolution
-------------------
Assume that an unconstrained formal cannot have its subelements associated on
an individual basis.


VASG-ISAC Analysis & Rationale
------------------------------
The LRM does not specifically address the issue of whether an unconstrained
formal (or local) can have its subelements associated on an individual basis.
Some implementors have inferred that subelement association is allowable in
this situation; others have concluded that it is illegal.  So, for VHDL87, the
use of such constructs may result in nonportable code.

However, there is agreement that it is reasonable to allow subelement
association in these cases.  Therefore, language should be added to the next
LRM revision to allow this.


VASG-ISAC Recommendation for IEEE Std 1076-1987
-----------------------------------------------
Not all implementations support subelement association for unconstrained
formals or locals.  Therefore, the use of such an association is nonportable.


VASG-ISAC Recommendation for Future Revisions
---------------------------------------------
Add appropriate wording to the LRM to the effect that subelement association
is allowed when the formal (or local) parameters are unconstrained arrays, and
that in such cases the direction of the range is that of the type of the formal
(or local) parameter and that the high and low bounds are determined from the
maximum and minimum indexes given in the subelement association.