VHDL Issue Number:      1042
Classification:         Language Definition Problem
Language Version:       VHDL-93
Summary:                Missing sentence for variable assignment aggregate
                        target.
Related Issues:         0221
Relevant LRM Sections:  8.5, 8.4
Key Words and Phrases:  form-of-aggregate target, variable assignments, 
                        "others"
Current Status:         ISAC-Approved
1076-1993 Disposition:  N/A
Disposition Rationale:  N/A
Superseded By:          N/A
-----------------------
Date Submitted:         1991/03/08
Author of Submission:   Laurence Groves (edited by Daniel Barclay)
Author's Affiliation:   Synopsys Inc.
Author's Post Address:  1098 Alta Ave.
                        Mountain View, CA 94043
Author's Phone Number:  (415) 962-5426
Author's Fax Number:    
Author's Net Address:   larry@Synopsys.COM
-----------------------
Date Analyzed:          1994/08/01
Author of Analysis:     Daniel S. Barclay
Revision Number:        $Revision: 1.9 $
Date Last Revised:      $Date: 1995/05/15 21:26:37 $


Description of Problem
----------------------
LRM Section 8.4, the fourth text paragraph states:

        If the target of a signal assignment statement is in the form of an
        aggregate, and the expression in an element association of that
        aggregate is a signal name that denotes a given signal, then the given
        signal and each subelement thereof (if any) are said to be identified
        by that element association as targets of the assignment statement.  It
        is an error if a given signal or any subelement thereof is identified
        as a target by more than one element association in such an aggregate.
        Furthermore, it is an error if an element association in such an
        aggregate contains an others choice or a choice that is a discrete
        range.

LRM Section 8.5, the fourth text paragraph states:

        If the target of a variable assignment statement is in the form of an
        aggregate, and  the locally static name in an element association of
        that aggregate denotes a given variable or denotes another variable of
        which the given variable is a subelement, then the element association
        is said to identify the given variable as a target of the assignment
        statement.  It is an error if a given variable is identified as a
        target by more than one element association in such an aggregate.

The rule/sentence (last sentence of LRM 8.4 paragraph 4):

        Furthermore, it is an error if an element association in such
        an aggregate contains an others choice or a choice that is a
        discrete range.

is missing from LRM Section 8.5, paragraph 4.


Proposed Resolution
-------------------
Add the missing sentence.


VASG-ISAC Analysis & Rationale
------------------------------
This does appear to be an unintentional omission.  

VHDL added the feature of form-of-aggregate targets relative to the base lan-
guage taken from Ada; this strongly implies that the missing sentence was 
not deleted intentionally.  

Additionally, form-of-aggregate targets probably were added for signals first.
(Temporary variables can be used in the sequential context to implement the
behavior of a variable assignment statement with a form-of-aggregate target, 
but there is no workaround for a concurrent signal assignment.)  Form-of-
aggregate targets for variable assignments probably were added later to be 
consistent with with signal assignments.  This is consistent with the sentence
being forgotten for variable assignments.

There does not appear to be any reason not to add the missing sentence.  The
statement

        (1 => v1, 2 => v2, others => v3) := "12345";

doesn't make much sense; would v3 get '3', '4', or '5'?  Relatedly, allowing
the statement

        (1 => v1, 2 => v2, others => v3) := "123";

doesn't add any functionality or significant convenience beyond the legal 
statement

        (1 => v1, 2 => v2, 3 => v3) := "123";


VASG-ISAC Recommendation for IEEE Std 1076-1987
-----------------------------------------------
Add the missing sentence as proposed:

        Furthermore, it is an error if an element association in such
        an aggregate contains an others choice or a choice that is a
        discrete range.


VASG-ISAC Recommendation for Future Revisions
---------------------------------------------
Add the missing sentence.  

Additionally, reword the enclosing paragraphs to remove unnecessary differ-
ences in wording ("expression in an element association" and "locally static 
name in an element association" refer to the same thing), and then remove 
all duplicate wording by having two references to one rule in the text.