VHDL Issue Number:      1043
Classification:         Language Definition Problem
Language Version:       VHDL-93
Summary:                User defined attribute on function name
Related Issues:         Supersedes 0222
Relevant LRM Sections:
Key Words and Phrases:
Current Status:         Analyzed
1076-1993 Disposition:  N/A
Disposition Rationale:  N/A
Superseded By:          N/A
-----------------------
Date Submitted:         1991/03/04
Author of Submission:   Laurence Groves
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:          1994/07/25
Author of Analysis:     John Willis
Revision Number:        $Revision: 1.2 $
Date Last Revised:      $Date: 1995/05/15 19:09:55 $


Description of Problem
----------------------
Consider the following:

    package P is
       function f return BIT_VECTOR;
       attribute length : integer;
       attribute length of f : function is 5;  -- is this allowed?
    end P;

When f'length is later used in a signal or variable assignment statement, or
anywhere else f'length is used, should f be interpreted as a function call,
in which case it is "appropriate for an array object" and thus the 'length is
the predefined attribute.  Or should it be interpreted as the name of a
function entity, in which case the 'length is the user defined attribute.


Proposed Resolution
-------------------
Interpret f as a function call and therefore f'length is the length of
the bit_vector returned by f.

Additionally, it is illegal for the user to attribute an object with an
attribute whose name conflicts with a predefined attribute of that object.


VASG-ISAC Analysis & Rationale
------------------------------
In this example, there are two valid interpretations of f'length, and 
thus the expression is ambiguous.  Unless one (or more) of the
interpretations can be eliminated by the context in which the expression
appears, the analyzer must report an ambiguous construct, which is an
error.


VASG-ISAC Recommendation for IEEE Std 1076-1993
-----------------------------------------------
No change recommended.


VASG-ISAC Recommendation for Future Revisions
---------------------------------------------
No change recommended.