Rationale for Ada 2012

John Barnes
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9.2.1 Incompatibilities with original Ada 2005

There are a small number of incompatibilities between the original Ada 2005 and that resulting from various corrections.
1 — The rules for full conformance have been strengthened; for example, null exclusions must now match. (AI-46, AI-134, AI-207, 6.3.1)
2 — When an inherited subprogram is implemented by a protected function, the first parameter has to be an in parameter, but not an access to variable type. Ada 2005 allowed access to variable parameters in this case; the parameter will need to be changed to access to constant by the addition of the constant keyword. (AI-291, 9.4)
3 — A missing rule is added that a limited with clause cannot name an ancestor unit. (AI-40, 10.1.2)
4 — Matching of formal access to subprogram types uses subtype conformance in Ada 2012 whereas it only used mode conformance in original Ada 2005. This change was necessary to avoid undefined behaviour in some situations. (AI-288, 12.5.4)
5 — An address attribute with a prefix of a subprogram with convention Intrinsic is now illegal. This is discussed in Section 6.6 of the chapter on Iterators, Pools etc. (AI-95, 13.3)
6 — Stream attributes must be specified by a static subprogram name rather than by a dynamic expression. (AI-39, 13.13.2)
7 — The use of discriminants on Unchecked_Union types is now illegal in record representation clauses. It makes no sense to specify the position of something that is not supposed to exist. (AI-26, B.3.3)
8 — A nonvolatile generic formal derived type precludes a volatile actual type. (AI-218, C.6)
9 — The restriction No_Relative_Delay has been extended to also prohibit a call of Timing_Events.Set_Handler with a Time_Span parameter. (AI-211, D.7)
10 — Various restrictions have been reworded to prevent the bypassing of the restriction by calling the forbidden subprogram via renames. (AI-211, D.7)

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