3.9 Defaults for generic formal types

Defaults for generic formal types (AI12-0205) provides easier and more natural generic instantiation. It uses the reserved words or use (see RM 12.5). For example:

generic
   type Item_Type is private;
   type Item_Count is range <> or use Natural;
                 --  New syntax using or use
   with function "=" (L, R : in Item_Type) return Boolean;
package Lists is
   ...
end Lists;

This allows the instantiator to be able to provide a type for the Item_Count, but it can simply be omitted in ordinary circumstances (in which case Natural would be used).