root/trunk/tendra/src/producers/ada/spec/SI99-0009-1.TXT

!standard 3.9.17                                      07-06-15  SI99-0009-1/04
!standard 17.1
!standard 17.20
!class binding interpretation 06-04-20
!status ARG Approved  11-0-0  07-06-02
!status work item 06-04-20
!status received 06-02-13
!priority High
!difficulty Easy
!qualifier Omission
!subject Handle new aggregate features

!summary

Update the semantics of Asis.Expressions.Component_Expression 
to handle this new association.

!question

The Amendment (Ada 2005) defines a new record and array component association with a box;
should ASIS be updated to correctly return these and associated expressions? (Yes.)

!recommendation

(See summary.)

!wording

Add A_Box_Expression after Not_An_Expression to type Expression_Kinds -- ASIS 3.9.17

    A_Box_Expression, -- 4.3.1(4), 4.3.3(3,6)

Add the following to the end bulleted list in ASIS section 17.1 (also, correct the penultimate
bullet to end with a period rather than a semicolon):

    * A_Box_Expression returned by Component_Expression applied to an unnormalized
      record association.

    AASIS Note: This is necessary as the <> of an unnnormalized record association
    may represent several components of different types. If the record association
    is normalized, it has a single component and the type of A_Box_Expression is
    that of the component. Similarly, the type of A_Box_Expression for an array
    association is that of the component type.

Add the following to ASIS section 17.20 (Component_Expression), just before
"Appropriate Association Kinds"


    For An_Array_Component_Association and non-normalized
    A_Record_Component_Association where the association contains a
    box expression, Asis.Expressions.Component_Expression
    returns A_Box_Expression. 

    For a normalized A_Record_Component_Association, where the association
    contains a a box expression, if the corresponding record type that
    contains this component contains a default expression,
    Asis.Expressions.Component_Expression returns this default
    expression, otherwise Asis.Expressions.Component_Expression
    returns A_Box_Expression.


!discussion

The appendix has the original proposal from Sergey Rybin on this topic.
At the Porto meeting it was decided that adding a A_Box_Expression to the
Expression_Kinds would better address this language feature, and would
avoid the problem of a Nil_Element being returned unnecessarily.

!appendix

Subject: Summary of the proposals for updating the ASIS Standard for Ada 2005
From: Sergey I. Rybin
Date: Mon, 13 Feb 2006 13:55:06 +0300

Formally the ASIS revision process is supposed to be started only after
finishing all the technical work with the new revision of the Ada Standard,
but I think we can start some preliminary technical work with new ASIS
definition already now (all the changes in Ada definition are stable
enough to start the ASIS revision).

At AdaCore we have developed a draft version of the new ASIS specification
and most of the proposed changes are already implemented in the latest
version of GNAT/ASIS technology. The attached file contains the summary
of the changes in the ASIS Standard we have made to adopt the new Ada
features. The interesting thing I've realized when working on
our draft of the new ASIS specification is that if we would like
to keep the upward compatibility as much as possible and if we
would like to keep changes as small as possible,
the new Ada definition gives us very limited freedom in making changes
in the ASIS spec. It does not mean that we think that our proposals
are the only possible solution for ASIS 2005, but it gives us some
hope that we can do ASIS revision for Ada 2005 fast enough.

There is quite a natural mapping of the proposed changes in the ASIS
specification onto the existing set of Ada Issues used for Ada revision,
and the attached file is structured and ordered by AIs. The only
exception is the new values in the ASIS Element Classification needed
to represent the new Ada 2005 predefined attributes and pragmas (of course,
this could be also mapped onto AIs, but I do not think that it would make
sense, because this is the easiest and completely straightforward part
of the ASIS revision).

My main goal of sending this ASIS 2005 Draft summary is to start
the ASIS 2005 discussion. The document itself would hardly be a convenient
background for this discussion - we will have at least split it on
changes related to different language issues, we will also have to
find a way for documenting the revision discussion, probably we
may need a separate mailing list for it. But let's get started!

Sergey Rybin


.....

--------------------------------
-- AI-287 Boxes in aggregates --
--------------------------------
RM-06 4.3.1, 4.3.3

* Define the semantics of An_Array_Component_Association and
  A_Record_Component_Association for the case if the argument association
  contains a box:

  - for An_Array_Component_Association and non-normalized
    A_Record_Component_Association Asis.Expressions.Component_Expression
    returns Nil_Element;

  - for Is_Normalized A_Record_Component_Association, in case if the
    corresponding record type contains for this component the default
    expression, Asis.Expressions.Component_Expression returns this default
    expression, and Asis.Expressions.Is_Defaulted_Association returns True for
    this A_Record_Component_Association, otherwise
    Asis.Expressions.Component_Expression returns Nil_Element

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