VHDL Issue Number:      1015
Classification:         Examples, Notes, and Appendices
Language Version:       VHDL-93
Summary:                The note illustrating the equivalent sequence of
                        declarations for a constrained array type definition is
                        in error.
Related Issues:         0105
Relevant LRM Sections:  3.2.1
Key Words and Phrases:  Constrained array types
Current Status:         Analyzed
-----------------------
1076-1993 Disposition:  N/A
Disposition Rationale:  N/A
Superseded By:          N/A
Date Submitted:         1988/06/04
Author of Submission:   Paul Menchini
Author's Affiliation:   Menchini Consultancy
Author's Post Address:  2 Davis Drive, P.O. Box 13036
                        Research Triangle Park, NC  27709-3036
Author's Phone Number:  (919) 990-9506
Author's Fax Number:    (919) 990-8561
Author's Net Address:   mench@mercury.interpath.net
-----------------------
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
----------------------
(This IR superseded IR 0105.)

The note at the end of Section 3.2.1, on Page 3-10, illustrating the sequence
of declarations equivalent to the constrained array type declaration shown in
the note is incorrect.  The relevant LRM text (on the bottom of Page 3-9)
reads:

    "A constrained array definition defines both an array type
     and a subtype of this type:

         *  The array type is an implicitly declared anonymous
        type; this type is defined by an (implicit)
        unconstrained array definition, in which the element
        subtype indication is that of the constrained array
        definition, and in which the type mark of each index
        subtype definition denotes the subtype defined by the
        corresponding discrete range.

         *  The array subtype is the subtype obtained by imposition
        of the index constraint on the array type."

This text defines two declarations, not the three shown in the note on Page
3-10.


Proposed Resolution
-------------------
Change the note to read:

    "The rules concerning constrained type declarations mean that
     a type declaration with a constrained array declaration such
     as

        type T is array (POSITIVE range MIN to MAX) of ELEMENT;

     is equivalent to the sequence of declarations

        type array_type is array (POSITIVE range <>) of ELEMENT;
        subtype T is array_type (MIN to MAX);

     where array_type is anonymous.  Consequently, T is the name of
     a subtype and all objects declared with this type mark are
     arrays that have the same index range.


VASG-ISAC Analysis & Rationale
------------------------------
The proposed note revision increases the consistency between the
precise definition and the example.  The change seems to make sense.


VASG-ISAC Recommendation for IEEE Std 1076-1993
-----------------------------------------------
None


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

As Paul suggests, change the note to read:

    "The rules concerning constrained type declarations mean that
     a type declaration with a constrained array declaration such
     as

        type T is array (POSITIVE range MIN to MAX) of ELEMENT;

     is equivalent to the sequence of declarations

        type array_type is array (POSITIVE range <>) of ELEMENT;
        subtype T is array_type (MIN to MAX);

     where array_type is anonymous.  Consequently, T is the name of
     a subtype and all objects declared with this type mark are
     arrays that have the same index range.