Rationale for Ada 2005: 2 Access types

This paper describes various improvements concerning access types for Ada 2005. Ada 2005 permits all access types to be access to constant types and to indicate that null is not an allowed value in all contexts. Anonymous access types are permitted in more contexts than just as access parameters and discriminants; they can also be used for variables and all components of composite types. This further use of access types is of considerable value in object oriented programming by reducing the need for (unnecessary) explicit type conversions. A further major improvement concerns access to subprogram types which are now allowed to be anonymous in line with access to object types. This permits so-called "downward closures" and allows the flexible use of procedures as parameters of subprograms and thereby avoids excessive use of generic units.