[multiple changes]

2011-11-23  Ed Schonberg  <schonberg@adacore.com>

	* exp_ch5.adb (Expand_Iterator_Loop): Wrap the expanded loop
	and the cursor declarations in a block, so that the loop variable
	is local to the construct.

2011-11-23  Matthew Heaney  <heaney@adacore.com>

	* a-coorma.ads, a-ciorma.ads, a-cborma.ads (Iterate): Returns
	type Reversible_Iterator'Class.
	* a-coorma.adb, a-ciorma.adb, a-cborma.adb (Iterator):
	Declare type as limited.
	(First, Last): Return value depends on iterator's start node value.
	(Next, Previous): Call corresponding Cursor-based operation.
	(Iterate): Indicate whether complete or partial iteration

From-SVN: r181659

1 files changed, 98 insertions, 18 deletions

diff --git a/gcc/ada/a-cborma.adb b/gcc/ada/a-cborma.adb
index 4cc2686bb22..940d6efa9cb 100644
--- a/gcc/ada/a-cborma.adb
+++ b/gcc/ada/a-cborma.adb
@@ -39,7 +39,7 @@ with System;  use type System.Address;
 
 package body Ada.Containers.Bounded_Ordered_Maps is
 
-   type Iterator is new
+   type Iterator is limited new
      Map_Iterator_Interfaces.Reversible_Iterator with record
         Container : Map_Access;
         Node      : Count_Type;
@@ -579,12 +579,24 @@ package body Ada.Containers.Bounded_Ordered_Maps is
    end First;
 
    function First (Object : Iterator) return Cursor is
-      F : constant Count_Type := Object.Container.First;
    begin
-      if F = 0 then
-         return No_Element;
+      --  The value of the iterator object's Node component influences the
+      --  behavior of the First (and Last) selector function.
+
+      --  When the Node component is 0, this means the iterator object was
+      --  constructed without a start expression, in which case the (forward)
+      --  iteration starts from the (logical) beginning of the entire sequence
+      --  of items (corresponding to Container.First, for a forward iterator).
+
+      --  Otherwise, this is iteration over a partial sequence of items. When
+      --  the Node component is positive, the iterator object was constructed
+      --  with a start expression, that specifies the position from which the
+      --  (forward) partial iteration begins.
+
+      if Object.Node = 0 then
+         return Bounded_Ordered_Maps.First (Object.Container.all);
       else
-         return Cursor'(Object.Container.all'Unchecked_Access, F);
+         return Cursor'(Object.Container, Object.Node);
       end if;
    end First;
 
@@ -886,22 +898,62 @@ package body Ada.Containers.Bounded_Ordered_Maps is
    end Iterate;
 
    function Iterate
-     (Container : Map) return Map_Iterator_Interfaces.Forward_Iterator'class
+     (Container : Map) return Map_Iterator_Interfaces.Reversible_Iterator'Class
    is
-      It : constant Iterator :=
-             (Container'Unrestricted_Access, Container.First);
    begin
-      return It;
+      --  The value of the Node component influences the behavior of the First
+      --  and Last selector functions of the iterator object. When the Node
+      --  component is 0 (as is the case here), this means the iterator object
+      --  was constructed without a start expression. This is a complete
+      --  iterator, meaning that the iteration starts from the (logical)
+      --  beginning of the sequence of items.
+
+      --  Note: For a forward iterator, Container.First is the beginning, and
+      --  for a reverse iterator, Container.Last is the beginning.
+
+      return Iterator'(Container'Unrestricted_Access, Node => 0);
    end Iterate;
 
    function Iterate
      (Container : Map;
       Start     : Cursor)
-      return Map_Iterator_Interfaces.Reversible_Iterator'class
+      return Map_Iterator_Interfaces.Reversible_Iterator'Class
    is
-      It : constant Iterator := (Container'Unrestricted_Access, Start.Node);
    begin
-      return It;
+
+      --  iterator was defined to behave the same as for a complete iterator,
+      --  and iterate over the entire sequence of items. However, those
+      --  semantics were unintuitive and arguably error-prone (it is too easy
+      --  to accidentally create an endless loop), and so they were changed,
+      --  per the ARG meeting in Denver on 2011/11. However, there was no
+      --  consensus about what positive meaning this corner case should have,
+      --  and so it was decided to simply raise an exception. This does imply,
+      --  however, that it is not possible to use a partial iterator to specify
+      --  an empty sequence of items.
+
+      if Start = No_Element then
+         raise Constraint_Error with
+           "Start position for iterator equals No_Element";
+      end if;
+
+      if Start.Container /= Container'Unrestricted_Access then
+         raise Program_Error with
+           "Start cursor of Iterate designates wrong map";
+      end if;
+
+      pragma Assert (Vet (Container, Start.Node),
+                     "Start cursor of Iterate is bad");
+
+      --  The value of the Node component influences the behavior of the First
+      --  and Last selector functions of the iterator object. When the Node
+      --  component is positive (as is the case here), it means that this
+      --  is a partial iteration, over a subset of the complete sequence of
+      --  items. The iterator object was constructed with a start expression,
+      --  indicating the position from which the iteration begins. (Note that
+      --  the start position has the same value irrespective of whether this
+      --  is a forward or reverse iteration.)
+
+      return Iterator'(Container'Unrestricted_Access, Node => Start.Node);
    end Iterate;
 
    ---------
@@ -935,12 +987,24 @@ package body Ada.Containers.Bounded_Ordered_Maps is
    end Last;
 
    function Last (Object : Iterator) return Cursor is
-      F : constant Count_Type := Object.Container.Last;
    begin
-      if F = 0 then
-         return No_Element;
+      --  The value of the iterator object's Node component influences the
+      --  behavior of the Last (and First) selector function.
+
+      --  When the Node component is 0, this means the iterator object was
+      --  constructed without a start expression, in which case the (reverse)
+      --  iteration starts from the (logical) beginning of the entire sequence
+      --  (corresponding to Container.Last, for a reverse iterator).
+
+      --  Otherwise, this is iteration over a partial sequence of items. When
+      --  the Node component is positive, the iterator object was constructed
+      --  with a start expression, that specifies the position from which the
+      --  (reverse) partial iteration begins.
+
+      if Object.Node = 0 then
+         return Bounded_Ordered_Maps.Last (Object.Container.all);
       else
-         return Cursor'(Object.Container.all'Unchecked_Access, F);
+         return Cursor'(Object.Container, Object.Node);
       end if;
    end Last;
 
@@ -1044,8 +1108,16 @@ package body Ada.Containers.Bounded_Ordered_Maps is
      (Object   : Iterator;
       Position : Cursor) return Cursor
    is
-      pragma Unreferenced (Object);
    begin
+      if Position.Container = null then
+         return No_Element;
+      end if;
+
+      if Position.Container /= Object.Container then
+         raise Program_Error with
+           "Position cursor of Next designates wrong map";
+      end if;
+
       return Next (Position);
    end Next;
 
@@ -1095,8 +1167,16 @@ package body Ada.Containers.Bounded_Ordered_Maps is
      (Object   : Iterator;
       Position : Cursor) return Cursor
    is
-      pragma Unreferenced (Object);
    begin
+      if Position.Container = null then
+         return No_Element;
+      end if;
+
+      if Position.Container /= Object.Container then
+         raise Program_Error with
+           "Position cursor of Previous designates wrong map";
+      end if;
+
       return Previous (Position);
    end Previous;