VHDL Issue Number:      0078
Classification:         Language Definition Problem
Language Version:       VHDL-87
Summary:                May locally static array subtype have a dynamic
                        element subtype?
Related Issues:         0096    
Relevant LRM Sections:  7.4, 8.7
Key Words and Phrases:  Case statement, locally static array subtype
Current Status:         VASG-Approved
1076-1993 Disposition:  Closed (All Issues Completely Addressed)
Disposition Rationale:  Section 8.8 (VHDL-93 LRM) was updated
Superseded By:          N/A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:          1989/09/01
Author of Analysis:     Doug Dunlop
Revision Number:        $Revision: 1.10 $
Date Last Revised:      $Date: 1995/08/03 17:18:01 $


Description of Problem
----------------------
LRM 8.7 states that if a case statement expression
is an object of a locally static subtype, then each value of the subtype must
be represented once and only once in the set of choices of the case statement,
and no other value is allowed.  The obvious intent here is to make this an
analysis-time check; this is not possible for locally static array subtypes
whose element subtype is not locally static.


Proposed Resolution
-------------------
For the time being, the check will not be performed for locally
static array subtypes whose element subtype is not locally static.


VASG-ISAC Analysis & Rationale
------------------------------
The natural first reaction to this problem is to say that a locally static
array subtype must have a locally static element type.  This would solve this
particular problem dealing with case statement indexing expressions.  More
broadly though, what are the true requirements on a locally static subtype?
What is the rationale behind the notion?  We have not been able to come with
good answers to these questions.  Rather than attempt to modify what appears
to be a dubious language concept to fix this specific case statement problem,
it seems preferable to re-work the requirements on the case statement indexing
expression and choices without making use of the concept of a locally static
array subtype.

IR-0096 points out a related problem concerning the case statement indexing
expressions.  These two problems should be remedied with a single re-statement
of the rules concerning these expressions and the case statement choices.


VASG-ISAC Recommendation for IEEE Std 1076-1987
-----------------------------------------------
Refer to IR-0096.


VASG-ISAC Recommendation for Future Revisions
---------------------------------------------
Refer to IR-0096.