VHDL Issue Number:      0164
Classification:         Language Definition Problem
Language Version:       VHDL-87
Summary:                Must others associations stand alone and last in an
                        aggregate?
Related Issues:         None.
Relevant LRM Sections:  7.3.2, 8.7
Key Words and Phrases:  others, association, choices
Current Status:         Submitted
1076-1993 Disposition:  Closed (All Issues Completely Addressed)
Disposition Rationale:  Section 7.3.2 was revised.
Superseded By:          N/A
-----------------------
Date Submitted:         1991/03/14
Author of Submission:   Paul Menchini
Author's Affiliation:   CAD Language Systems, Inc.
Author's Post Address:  P.O. Box 13036
                        Research Triangle Park, NC  27709-3036
Author's Phone Number:  (919) 361-1913
Author's Fax Number:    
Author's Net Address:   mench@clsi.com
-----------------------
Date Analyzed:          TBD
Author of Analysis:     TBD
Revision Number:        $Revision: 1.9 $
Date Last Revised:      $Date: 1995/08/04 01:43:10 $


Description of Problem
----------------------
Section 7.3.2 defines the element association of aggregates as follows:

        element_association ::=
                [ choices => ] expression

        choices ::= choice { | choice }

        choice ::=
                simple_expression
                | discrete_range
                | *element*_simple_name
                | OTHERS

This BNF allows an element association of the form "3 | 7 to 17 | others => 5".
Is there a semantic restriction that disallows this element association?
Paragraph 3 of the same section states "... no element associations may follow
an OTHERS association....", and paragraph 4 states "An element association with
the single choice OTHERS is allowed....", but neither statement explicitly
disallows the example element association.

The wording in this section was reworked from Ada's corresponding section
(4.3); in that process, the following sentence from paragraph 5 of this section
of the Ada LRM was inverted to form the sentence from paragraph 4 of
the VHDL LRM:

        The choice OTHERS is only allowed in a component association if
        the association appears last and has this single choice; ....

The Ada language seems clearer.

Moreover, Section 8.7 (of the VHDL LRM) explicitly states that OTHERS as a case
statement alternative must be the last such alternative and that OTHERS must be
the only choice in the alternative.


Proposed Resolution
-------------------
Explicitly prohibit others from being one choice among many in a single element
association.


VASG-ISAC Analysis & Rationale
------------------------------
TBD


VASG-ISAC Recommendation for IEEE Std 1076-1987
-----------------------------------------------
TBD


VASG-ISAC Recommendation for Future Revisions
---------------------------------------------
TBD