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Ada 2005 Rationale – Access types (pt 3 of 8)
Thursday February 2, 2006
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.
This is one of a number of papers concerning Ada 2005 which are being published in the
Ada User Journal. An earlier version of this paper appeared in the Ada User Journal, Vol.
26, Number 2, June 2005. Other papers in this series will be found in later issues of the
Journal or elsewhere on this website.
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in Ada / Ada 2005, Technical Papers