formal array types and default values

[Mehdi Saada <00120260a@gmail.com>]

I have several questions more or less related.
First: why aspect DEFAULT_COMPONENT_VALUE can apply only to components of scalar type ? It would be nice to be able to set a default value to an array type in a generic package, equal to a generic object parameter.

type T_Vect_Coef is array (T_Degre range <>) of ELEMENT;
gives that message:
main.adb:21:22: unconstrained subtype not allowed (need initialization)
main.adb:21:22: provide initial value or explicit array bounds

ELEMENT and T_DEGRE are generic and declared like that:
type ELEMENT is private;
type T_DEGRE is range <>;

Those two types are public. How can I give a default value, since DEFAULT_COMPONENT_VALUE doesn't apply to non scalar types.

In the private part,
the type
type T_Polynome (Degre : T_Degre := 0) is -- type mutant
    record
        COEF : T_Vect_Coef (0..Degre) := (others => NULL_ELEMENT);
    end record;
gives that warning: creation of "T_Polynome" object may raise Storage_Error. Why?