!standard 4.1.5(5.1/4)                                    16-11-10  AI12-0203-1/02
!standard 4.1.5(7/3)
!class presentation 16-10-06
!status Amendment 1-2012 16-11-10
!status ARG Approved 10-0-0  16-10-08
!status work item 16-10-06
!status received 16-09-08
!priority Low
!difficulty Easy
!qualifier Clarification
!subject Overriding a nonoverridable aspect
!summary

Clarify 4.1.5(7/3).

!question

4.1.5(5.1/4) says:

   The Implicit_Dereference aspect is nonoverridable (see 13.1.1).

while 4.1.5(7/3) starts:

   Given a reference type T, the Implicit_Dereference aspect is
   inherited by descendants of type T if not overridden. 

Since the aspect can't be overridden, why the "if not overridden" above?

!recommendation

A nonoverridable aspect can have a confirming aspect value specified,
and that is the case that has to be covered by the 4.1.5(7/3) sentence.
A clarification is suggested.

(See Summary.)

!wording

Modify 4.1.5(7/3):

   Given a reference type T, the Implicit_Dereference aspect is inherited
   by descendants of type T if not overridden{ Redundant[(which is only
   permitted if confirming)]}. If a descendant type constrains the value of
   the reference discriminant of T by a new discriminant, that new
   discriminant is the reference discriminant of the descendant.
   Redundant[If the descendant type
   constrains the value of the reference discriminant of T by an expression
   other than the name of a new discriminant, a generalized_reference that
   identifies an object of the descendant type denotes the object or
   subprogram designated by the value of this constraining expression.]

!discussion

(See !recommendation.)

!corrigendum 4.1.5(7/3)

@drepl
Given a reference type @i<T>, the Implicit_Dereference aspect is inherited by
descendants of type @i<T> if not overridden. If a descendant type constrains
the value of the reference discriminant of @i<T> by a new discriminant, that
new discriminant is the reference discriminant of the descendant. If the
descendant type constrains the value of the reference discriminant of @i<T> by
an @fa<expression> other than the @fa<name> of a new discriminant, a
@fa<generalized_reference> that identifies an object of the descendant type
denotes the object or subprogram designated by the value of this constraining
expression.
@dby
Given a reference type @i<T>, the Implicit_Dereference aspect is inherited by
descendants of type @i<T> if not overridden (which is only permitted if
confirming). If a descendant type constrains
the value of the reference discriminant of @i<T> by a new discriminant, that
new discriminant is the reference discriminant of the descendant. If the
descendant type constrains the value of the reference discriminant of @i<T> by
an @fa<expression> other than the @fa<name> of a new discriminant, a
@fa<generalized_reference> that identifies an object of the descendant type
denotes the object or subprogram designated by the value of this constraining
expression.

!ASIS

No ASIS effect.

!ACATS test

No ACATS test needed.

!appendix

The original issue was raised privately by Steve Baird; another AdaCore
person independently raised the issue a few days later. The wording was
suggested by Tucker Taft.

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