VHDL Issue Number:        2122

Language_Version          VHDL-2002
Classification            Language Modeling Enhancement or Deficiency
Summary                   Protected method has implied object parameter?
Relevant_LRM_Sections     3.5.1 Protected type declarations
                          2.4.2 Signatures
Related_Issues           
Key_Words_and_Phrases     protected type
                          method
                          signature
                          overload resolution
Authors_Name              James Unterburger
Authors_Phone_Number      503-685-0860
Authors_Fax_Number       
Authors_Email_Address     jamesu@model.com
Authors_Affiliation       Mentor Graphics
Authors_Address1          8005 SW Boeckman Rd.
Authors_Address2          Wilsonville, OR 97070
Authors_Address3         

Current Status:           Submitted

Superseded By:

------------------------
Date Submitted:           7 September 2007
Date Analyzed:		  8 October 2007
Author of Analysis:	  Peter Ashenden
Revision Number:          1
Date Last Revised:	  8 October 2007

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

In discussing methods, the text states "In addition to the (implied)
object of the protected type operated on by the subprogram, additional
parameters may be explicitly specified in the formal parameter list of
the subprogram declaration of the subprogram".
   
The word "additional" suggests that the protected type object to be
operated on is somehow an implied formal to the subprogram.  Also, the
fact that nested protected types are legal suggests that there are
actually N implied objects being operated on where N is the nesting
level of where the method is.
   
Do the implied objects/formals come into play for overloaded
subprogram resolution?  Do their (protected) type names appear in the
signature of the subprogram?
   
In the following example, which "foo" is called when elaborating the
"v2" object?
   
    package pkg is
      function foo(x : string := "PKG") return string;
      type prot is protected
        function foo(x : string := "PROT") return string;
      end protected;
    end;
   
    package body pkg is
      type prot is protected body
        constant v : string(1 to 5) := "Hello";
        function foo(x : string := "PROT") return string is
        begin
          return v & x;
        end;
        variable v2 : string(1 to 5) := foo;
        variable ccc : string(1 to 10) := foo'path_name;
      end protected body;
      function foo(x : string := "PKG") return string is
      begin
        return "PKG " & x;
      end;
    end;
   

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



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

The submitter is makes a reasonable interpretation of the text of
3.5.1 as implying that the object of the protected type is a parameter
of a method. However, that is not the intention. The object of the
protected type is accessible to the subprogram by virtue of being the
enclosing declarative region in the elaborated design hierarchy. In
other words, the object is part of the closure of the subprogram. There
is no need to treat the object as an implicit parameter. The text in
3.5.1 should be amended to avoid the interpretation made by the
submitter.

Given that an object of a protected type is not to be considered as a
parameter of the protected type's methods, the protected type does not
occur in the parameter type profiles of the methods, nor does it
appear in a matching signature for any of the methods. Only the
explicitly listed parameter types occur in the parameter type profile
and signature for a method. If the text of 3.5.1 is amended to avoid
mention of implicit parameters, there is no need to amend the text of
2.3 or 2.3.2.

In the submitter's example, the function foo declared immediately
within the package and the function foo declared as a method of the
protected type are homographs. Hence, within the scope of the method,
the function declared in the package is hidden. That includes the
declaration of v2, so the method foo is called when elaborating v2.



VASG-ISAC Recommendation for IEEE Std 1076-2002
-----------------------------------------------

Interpret the second sentence in the second paragraph of page 51 in
3.5.1 as though the text "(implied)" and "additional" were deleted.

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

In the second paragraph of page 51 in 3.5.1, delete the text
"(implied)" and "additional", so that the sentence reads:

  In addition to the object of the protected type operated on by the
  subprogram, parameters may be explicitly specified in the formal
  parameter list of the subprogram declaration of the subprogram.