Rationale for Ada 2005
2.2 Reserved words
Ada 2005 has three further reserved words namely
, and synchronized
may recall that Ada 95 had six more reserved words than Ada 83 and the
fact that this meant that some programs were incompatible and thus had
to be rewritten loomed large in the minds of many commentators.
When new syntax for the introduction of interfaces
was being discussed it was strongly felt that incompatibilities should
be avoided and that any new syntax words should be unreserved. It was
also noted that Interface was a popular identifier
and that making it a reserved word would cause many programs to have
to be rewritten.
However, it was soon
realised that treating Interface as unreserved
would have permitted sequences such as
type T is interface;
subtype Interface is T;
in which Interface is
a subtype of the interface T. This would have
been total madness. Some reviewers also had memories of PL/I in which
words such as IF were not reserved so that one could write IF IF ...
where the first IF is a syntax word and the second is a user identifier.
Accordingly it was decided that the new words would
have to be reserved. No sensible alternative to interface could
be thought of although it would be irritating for users who had packages
called Interface – actually a brief
survey revealed that most such packages had longer names such as Radar_Interface
so that the problem was more apparent than real. The other new reserved
words overriding and synchronized clearly present less
of a problem since they are less likely to have been used as identifiers.
© 2005, 2006, 2007 John Barnes Informatics.
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