CVS difference for ai12s/ai12-0377-1.txt
--- ai12s/ai12-0377-1.txt 2020/06/08 00:25:36 1.7
+++ ai12s/ai12-0377-1.txt 2020/06/17 00:20:22 1.8
@@ -1,9 +1,11 @@
-!standard 6.4.1(5.1/4) 20-06-07 AI12-0377-1/02
+!standard 6.4.1(5.1/4) 20-06-15 AI12-0377-1/03
-!class Amendment 20-04-20
+!class binding interpretation 20-06-13
+!status Amendment 1-2012 20-06-15
+!status ARG Approved 13-0-0 20-06-13
!status work item 20-04-20
!status received 20-04-14
@@ -16,7 +18,7 @@
not. Program_Error is raised if this occurs where one of the types is a
generic formal type.
Consider this example:
@@ -49,8 +51,10 @@
object, which is the sort of thing that shouldn't normally be possible for an
object whose type has a specified Default_Value.
+Should this be revisited? (Yes.)
@@ -90,18 +94,21 @@
"Deinitialization" here cannot introduce an invalid value into an object
-that the compiler assumed to be valid (the conversion back to
+that the compiler assumed to be valid; the conversion back to
the actual would still do a subtype check, which would cause Constraint_Error
if the value is invalid. Note that the check would be required since one
-cannot assume anything about out parameters). Even so, it seems dangerous
-enough that we should take steps to prevent it.
+cannot assume anything about out parameters. Even so, it seems dangerous
+enough that we should take steps to prevent it. AI12-0074-1 has examples
+of "deinitialization" causing problems, particularly with "unused" out
+parameters which only return values in some cases.
The best solution is to make any view conversion used in an out parameter
illegal if one type has Default_Value and the other does not. Note
that the repeal of 13.1(10/3) by AI12-0376-1 means that having the types be
related no longer prevents problems (as a derived type can define a
Default_Value when the parent type does not have one), so we would have to do
-something with this rule in any case.
+something with this rule in any case. The relationship still has value, though
+as the set of values will still be related.
The alternative of passing the default value in problematic cases would make
the deinitialization noted in the problem worse (since it would clobber the
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