CVS difference for ai05s/ai05-0282-1.txt

--- ai05s/ai05-0282-1.txt	2011/12/31 00:32:00	1.2
+++ ai05s/ai05-0282-1.txt	2011/12/31 01:36:38	1.3
@@ -1,5 +1,7 @@
-!standard 4.3.2(8)                                            11-11-13  AI05-0282-1/02
+!standard 4.3.2(8)                                            11-12-30  AI05-0282-1/03
 !class binding interpretation 11-11-08
+!status Amendment 2012 11-12-30
+!status ARG Approved  6-0-2  11-11-13
 !status work item 11-11-08
 !status received 11-09-26
 !priority Low
@@ -9,7 +11,8 @@
 
 !summary
 
-** TBD.
+4.3.2(8) applies when the ancestor of an extension aggreate is
+constraint.
 
 !question
 
@@ -37,26 +40,10 @@
 
 !recommendation
 
-** TBD.
+(See summary.)
 
 !wording
 
-In 4.3.2(7), replace:
-   are initialized by default as for an object of the ancestor type.
-with
-   are initialized by default as for an object of the subtype denoted
-   by the subtype_mark.
-
-and append a new paragraph:
-
-   If the type of the ancestor_part has discriminants and the
-   ancestor_part is a subtype_mark that denotes an unconstrained
-   subtype, each discriminant of the ancestor type
-   has the value specified for a corresponding discriminant, either in
-   the record_component_association_list, or in the
-   derived_type_definition or some ancestor of the type of
-   the extension_aggregate.
-
 Replace 4.3.2(8):
   If the type of the ancestor_part has discriminants that are not
   inherited by the type of the extension_aggregate, then, unless the
@@ -71,17 +58,15 @@
 
   If the type of the ancestor_part has discriminants and the
   ancestor_part is not a subtype_mark that denotes an unconstrained
-  subtype, then a check is made that each discriminant of the ancestor
-  has the value specified for a corresponding  discriminant, either
-  in the record_component_association_list, or in the
-  derived_type_definition for some ancestor of the type of
-  the extension_aggregate. Constraint_Error is raised if this check
-  fails.
+  subtype, then a check is made that each discriminant determined by
+  the ancestor part has the value specified for a corresponding discriminant,
+  if any, either in the record_component_association_list, or in the
+  derived_type_definition for some ancestor of the type of the
+  extension_aggregate. Constraint_Error is raised if this check fails.
 
 !discussion
 
-In order to help understand this wording, I think it helps to realize that
-if the ancestor type of an extension aggregate has discriminants, then there
+If the ancestor type of an extension aggregate has discriminants, then there
 are 6 cases to consider: the cross-product of whether the discriminants of
 the ancestor type are inherited by the type of the extension aggregate (yes
 or no) and the three possible forms of the ancestor part:
@@ -89,9 +74,47 @@
     a subtype mark denoting a constrained subtype
     a subtype mark denoting an unconstrained subtype.
 
+Keep in mind that an inherited discriminant might correspond to itself.
+
+This change is technically inconsistent with Ada 2005. An extension_aggregate
+with an ancestor_part whose discriminants are constrained and inherited might now
+raise Constraint_Error if the aggregate's type is constrained, while it was OK in
+Ada 2005. In almost all cases, this will make no difference as the constraint will
+be checked by the immediately following use of the aggregate, but it is possible to
+compare such an aggregate for equality; in this case, no exception would be raised
+by Ada 2005, while Ada 2012 will raise Constraint_Error. This should be very rare,
+and having the possibility means that the representation of the aggregate type has
+to be able to support unconstrained values of the type, even if the first subtype
+is constrained and no such objects can be created any other way. This is too costly
+to allow for such an unlikely case.
+
+!corrigendum 4.3.2(8)
+
+@drepl
+If the type of the @fa<ancestor_part> has discriminants that are not inherited
+by the type of the @fa<extension_aggregate>, then, unless the @fa<ancestor_part>
+is a @fa<subtype_mark> that denotes an unconstrained subtype, a check is made
+that each discriminant of the ancestor has the value specified for a corresponding
+discriminant, either in the @fa<record_component_association_list>, or in the
+@fa<derived_type_definition> for some ancestor of the type of the
+@fa<extension_aggregate>. Constraint_Error is raised if this check fails. 
+@dby
+If the type of the @fa<ancestor_part> has discriminants and the
+@fa<ancestor_part> is not a @fa<subtype_mark> that denotes an unconstrained
+subtype, then a check is made that each discriminant determined by
+the @fa<ancestor_part> has the value specified for a corresponding discriminant,
+if any, either in the @fa<record_component_association_list>, or in the
+@fa<derived_type_definition> for some ancestor of the type of the
+@fa<extension_aggregate>. Constraint_Error is raised if this check fails.
+
+
 !ACATS Test
 
+Create an ACATS C-Test similar to the example in the question.
+
 !ASIS
+
+No ASIS impact.
 
 !appendix