CVS difference for ai05s/ai05-0023-1.txt

--- ai05s/ai05-0023-1.txt	2007/04/11 00:57:09	1.3
+++ ai05s/ai05-0023-1.txt	2007/05/05 01:39:14	1.4
@@ -1,4 +1,4 @@
-!standard 13.13.2(9/2)                                   07-04-05    AI05-0023-1/02
+!standard 13.13.2(9/2)                                   07-04-19    AI05-0023-1/03
 !class binding interpretation 06-11-13
 !status work item 06-11-13
 !status received 06-06-27
@@ -44,28 +44,30 @@
 
 !wording
 
-Add after 13.13.2(9/2) 
+Add after 13.13.2(9/2):
 
     If T is a discriminated type and its discriminants have defaults then
     S'Read first reads the discriminants from the stream without modifying
     Item. S'Read then creates an object of type T constrained by these
-    discriminants. The Read attribute for each non-discriminant component
-    of this object (not of Item) is then called in canonical
-    order as described above. Finally, the value of this object is
-    converted to the subtype of Item and is assigned to Item. Normal default
-    initialization and finalization take place for this object.   
+    discriminants. The value of this object is then converted to the subtype
+    of Item and is assigned to Item. Finally, the Read attribute for each
+    non-discriminant component of Item is then called in canonical
+    order as described above. Normal default initialization and finalization
+    take place for the created object.   
     
-In 13.13.2(27/2) replace
+In 13.13.2(27/2) replace:
     S'Input then creates an object...
-with
+with:
     S'Input then creates an object of type T...
 
-Append to the end of 13.13.2(27/2)
+
+Append to the end of 13.13.2(27/2):
     If T has discriminants, then this object is constrained if and only if
-    T has discriminants without defaults (that is, if and only if discriminants
-    were read from the stream).
+    T has discriminants without defaults (that is, if and only if
+    discriminants were read from the stream).
+
 
-Add after 13.13.2(38)
+Add after 13.13.2(38):
 
          Implementation Permissions
          
@@ -93,23 +95,62 @@
           the stream are read from Item instead. 
         - The permissions of the preceding paragraph then apply and no object
           of type T need be created by the execution of S'Read.
-    
-Questions:
-1) When we say that "the value of this object ... is assigned to Item",
-   does it need to be explicitly stated that this is an assignment operation?
-   Does the list of assignment operations in 5.2(3) need to be updated? I
-   think not.
-   
-2) Does it need to be stated more explicitly that the permission to treat a
-   type with defaults as though it does not have defaults only applies in
-   the case where S'Input calls S'Read and does not apply in the case
-   where some other caller calls S'Read?
-
+          
+!example
 
+  declare
+    Counter : Natural := 0;
+    
+    function Default_Value return Integer is
+    begin
+      Text_Io.Put_Line ("F was called"); -- a user-visible side-effect
+      Counter := Counter + 1; -- another side-effect
+      return Counter;
+    end Default_Value;
+    
+    type R (D : Boolean := True) is
+      record
+        F : Integer := Default_Value;
+      end record;
+      
+    procedure P (Stream : access Ada.Streams.Root_Stream_Type'Class) is
+      Saved_Counter : constant Natural := Counter;
+      R_Val : constant R := (D => False, F => 123);
+    begin
+      R'Output (Stream, R_Val);
+      pragma Assert (R_Val = R'Input (Stream);
+      pragma Assert ((Counter - Saved_Counter) in 1 .. 2);
+    end;
+    
+    procedure Do_Some_Stuff_Including_A_Call_To_P is ... ;
+  begin
+    Do_Some_Stuff_Including_A_Call_To_P;
+  end;
+  
+Without these implementation permissions, the execution of P's call to
+R'Input must include two calls to Default_Value. R'Input would declare
+a local temporary and initialize it; this initialization would include
+one call to Default_Value. R'Input would then call R'Read, which would
+declare a second temporary and initialize it; this initialization would
+include the second call to Default_Value.
+
+With these implementation permissions, it is permitted to call
+Default_Value only once. 
+                    
 !discussion
 
 This problem applies to all depends-on-discriminant components with non-trivial
 finalization.
+
+When we say that "the value of this object ... is assigned to Item",
+does it need to be explicitly stated that this is an assignment operation?
+Does the list of assignment operations in 5.2(3) need to be updated? I
+think not.
+   
+Does it need to be stated more explicitly that the permission to treat a
+type with defaults as though it does not have defaults only applies in
+the case where S'Input calls S'Read and does not apply in the case
+where some other caller calls S'Read?
 
 
 --!corrigendum A.18.2(239/2)