Re: Bounds of Slice's return value

["Matthew Heaney" <mheaney@on2.com>]

"Matthew Woodcraft" <mattheww@chiark.greenend.org.uk> wrote in message
news:87bsfrcksf.fsf@chiark.greenend.org.uk...
> In particular, if I run the following program, should I always get '1',
> or is an implementation allowed to choose a different value?
>
> procedure Slice_Return_Value is
>    U : Unbounded_String := To_Unbounded_String ("hello");
>    S : String := Slice (U, 2, 3);
> begin
>    Put_Line (Integer'Image (S'first));
> end Slice_Return_Value;

You can fix this to specify the index constraint you desire, using a subtype
constraint:

declare
   F : constant Positive := 2;
   L : constant Positive := 3;
   S : constant String (1 .. L - F + 1) := Slice (U, F, L);
begin

or

declare
   F : constant Positive := 2;
   L : constant Positive := 3;
   S : constant String (F .. L) := Slice (U, F, L);
begin

Of course, this declares a constrained string object (no dope vector is
generated), so this is not strictly comparable to your original example.
You could fix that by using an explicit subtype:

declare
   F : constant Positive := 2;
   L : constant Positive := 3;
   subtype T is String (1 .. L - F + 1);
   S : constant String := T(Slice (U, F, L));
begin

or

declare
   F : constant Positive := 2;
   L : constant Positive := 3;
   subtype T is String (F .. L);
   S : constant String := T(Slice (U, F, L));
begin