Re: Discriminated types with default discriminants

["Martin Krischik" <krischik@users.sourceforge.net>]

Am 03.11.2005, 17:50 Uhr, schrieb Maciej Sobczak <no.spam@no.spam.com>:

> Hi,
>
> Consider this:
>
> procedure Hello is
>
>     type Discriminated(Size : Integer := 10) is
>        record
>           Value : String (1..Size);
>        end record;
>
>     S : Discriminated;
>
> begin
>     null;
> end Hello;
>
>
> Compiler (GNAT) gives me two warnings:
>
>       5.          Value : String (1..Size);
>                                      |
>          >>> warning: creation of object of this type may raise  
> Storage_Error
>
>       8.    S : Discriminated;
>             |
>          >>> warning: Storage_Error will be raised at run-time
>
>
> Moreover, it keeps a promise and indeed the program raises STORAGE_ERROR  
> at run-time.
>
> What's happening here? Why the object S is not created with 10 as the  
> default discriminant?

Because you might store a larger object later. So - at least GNAT -  
allocate as much memory as needed for the larges possible object - thats 2  
GB.

Hint 1: unless this is homework: use Bounded_String or Unbounded_String -  
don't reinvent the wheel.

Hint 2: try "type MyInt is range 0 .. 1000;" or whatever upper limit is  
sensible.

Martin

Links:
   http://en.wikibooks.org/wiki/Ada_Programming/Strings