VHDL Issue Number:  2030

Language_Version:   VHDL-2002
Classification:     Language Definition Problem
Summary:            What signature does a method have
Relevant_LRM_Sections:  3.5.1 a method operates on the "implied"
    protected type object the method is called from.
                        2.3.2 the signature is formed from the
    parameters and return type of subprogram decls
Related_Issues: 
Key_Words_and_Phrases:  protected, signature, method, subprogram,
                        procedure, function
Authors_Name:           Garland Bayley
Authors_Phone_Number:   503 685 4784
Authors_Fax_Number:     503 685 0921
Authors_Email_Address:  garlandb@model.com
Authors_Affiliation:    Model Technology
Authors_Address1:       8005 SW Boeckman Road
Authors_Address2:   
Authors_Address3:       Wilsonville, OR 97070

Current Status:         VASG-Approved

Superseded By:

------------------------
Date Submitted:     23 October 103
Date Analyzed:      15 July 2004
Author of Analysis: Peter Ashenden
Revision Number:    3
Date Last Revised:  09 May 2005

Description of Problem
----------------------

Since the method operates on the protected object, does that make it
part of the signature?  Is the signature of method p below p[] or
p[pt]?
    
Given

    attribute is_method:boolean;
    type pt is protected
     procedure p;
    end
    procedure p;
    procedure p(v :
    inout pt);
    attribute is_method of p[]:procedure is false;
    attribute is_method of p[pt]:procedure is true;
    
Which procedures p are attributed with true and which with false?
    
What about

    type pt is protected body
     procedure p is begin end;
     procedure p(v: inout pt) is begin end;
     attribute is_method of p[pt]:procedure is true;
    end;
    
What procedures get this latest attribute specification?
    

Proposed Resolution
-------------------

I would suggest signatures be changed to

    signature::=[[[protected]type_mark{,type_mark}][return type_mark]]

where methods get the reserved worked protected before the "implied"
protected type object the method is called from.

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

A method of a protected type is a subprogram declared within the
declarative region defined by the protected type declaration together
with with corresponding protected type body.  The signature of such a
method is defined by clause 2.3.2, and includes just the type marks
corresponding to each explicit parameter of the method (if any) and
the return type (if the method is a function).

While implementations may provide a method with access to the state of
the protected object via an implicit parameter, the LRM defines such
access in terms of scope and visibility rules.  A method of a specific
instance of a protected type is identified using an expanded name with
the instance name as a prefix and the method name as the suffix.  By
virtue of being elaborated as part of the protected type instance, the
method has visibility of the corresponding instance of the declared
items within the protected type instance.

The rules governing decoration of a method with an attribute are
described in clause 5.1.  Only a method declaration, not a method
body, can be decorated.  The attribute specification must occurr
immediately within the same declarative part as the method
declaration, that is, immediately within the protected type
declaration.

In the case of the reporter's examples (revised for correct syntax):

    attribute is_method: boolean;

    type pt is protected
     procedure p;  -- 1
    end protected;

    procedure p;  -- 2
    procedure p(v: inout pt);  -- 3

    attribute is_method of p[]:procedure is false;
    attribute is_method of p[pt]:procedure is true;

Here, the first attribute specification decorates procedure 2, and the
second attribute specification decorates procedure 3.

    type pt is protected body
     procedure p is begin end;  -- 4
     procedure p(v: inout pt) is begin end;  -- 5
     attribute is_method of p[pt]:procedure is true;
    end protected body;

Here, the attribute specification within the protected type body
decorates procedure 5.


VASG-ISAC Recommendation for IEEE Std 1076-2002
-----------------------------------------------
No change to the LRM

VASG-ISAC Recommendation for Future Revisions
---------------------------------------------
No change to the LRM


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