VHDL Issue Number:      0049
Classification:         Language Definition Problem
Language Version:       VHDL-87
Summary:                Exception for null array is missing in type
                        conversion description.
Related Issues:
Relevant LRM Sections:  7.3.5
Key Words and Phrases:  Null array, type conversion
Current Status:         ISAC-Approved
1076-1993 Disposition:  Closed (All Issues Completely Addressed)
Disposition Rationale:  The change was included in point b of section 7.3.5.
Superseded By:          N/A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:          1990/10/02
Author of Analysis:     Clive R. Charlwood
Revision Number:        $Revision: 1.7 $
Date Last Revised:      $Date: 1995/05/13 19:34:42 $


Description of Problem
----------------------
When null arrays were added to the language, a case where
an exception should be made for a null array was overlooked.  Specifically, in
LRM 7.3.5, the sentence that reads

   "If the type mark denotes an unconstrained array type, then, for each index
    position, a check is made that ...".

should read

   "If the type mark denotes an unconstrained array type and if the operand is
    not a null array, then, for each index position, a check is made that ..."

This change makes this aspect of type conversions similar to those in Ada.  The
VHDL language is inconsistent without this change.


Proposed Resolution
-------------------
This change is assumed.


VASG-ISAC Analysis & Rationale
------------------------------
The above description of the problem is correct.
The proposed solution should be accepted.


VASG-ISAC Recommendation for IEEE Std 1076-1987
-----------------------------------------------
Assume the paragraph

   "If the type mark denotes an unconstrained array type, then, for each index
    position, a check is made that ...".

reads as

   "If the type mark denotes an unconstrained array type and if the operand is
    not a null array, then, for each index position, a check is made that ..."


VASG-ISAC Recommendation for Future Revisions
---------------------------------------------
Codify the above assumption by updating the LRM.