Re: Discriminated record question

[Emmanuel Briot <briot@act-europe.fr>]

Mark.Doherty@uk.thalesgroup.com (Mark Doherty) writes:

> Why does the following raise a constraint error on the declaration of
> 'B'.
> 
> procedure Test is
>     type A_Type (Text_Size : Natural := 0) is
>        record
>             Text : String (1 .. 0);
>         end record;
>     A : A_Type;
> 
>     type B_Type (Text_Size : Natural := 0) is
>         record
>             Text : String (1 .. Text_Size);
>         end record;
> 
>     B : B_Type;  
> 
> begin
>     null;
> end Test;



Because when you specify a default value for the discriminant, the compiler
must allocate the maximum possible size (in that case Natural'Last), so you are
trying to declare a huge variable, which raises CE. I thought it would have
raised Storage_Error, but it might be compiler-dependent


Compiling the code above with GNAT gives a proper warning

gcc -c t8.adb
t8.adb:10:33: warning: creation of object of this type may raise Storage_Error
t8.adb:13:05: warning: Storage_Error will be raised at run-time
gnatbind -x t8.ali
gnatlink t8.ali