wrote in message news:alpine.DEB.2.20.1604062240350.29458@debian... On Wed, 6 Apr 2016, ahlan@marriott.org wrote: > In the annotated RM, in the section concerning Null Procedures, it says > "There are no null functions because the return value has to be > constructed somehow; a function that always raises Program_Error doesn't > seem very useful or worth the complication" If there are no null > functions because a return value has to be constructed then surely the > same applies to null procedures that have out parameters. These too > should be prohibited [...] This seems to be right. It does not make much sense to allow the declaration of procedure X(Formal: out T) is null; while prohibiting the declaration of function Y return R is null; The point is, you can neither call X nor Y. Semantically, both statements X(Actual); Actual := Y; are equally useless, or at least their effect is equally undefined. Allowing the declaration of X, but prohibiting the declaration of Y is inconsistent. If people really think they need to declare something like the above procedure X, a revised Ada standard could allow declarations such as procedure X(Formal: T) is raise; and function Y return T is raise; where "is raise" stands for "raise Program_Error". That may sometimes come handy in the context of inheritance, or so. -------- I love the taste of Cryptanalysis in the morning! -------- www.uni-weimar.de/de/medien/professuren/mediensicherheit/people/stefan-lucks ----Stefan.Lucks (at) uni-weimar.de, Bauhaus-Universität Weimar, Germany----