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From: stt@inmet.inmet.com
Newsgroups: comp.lang.ada
Subject: Re: implicit array type conversion
Message-ID: <20600056@inmet>
Date: 27 Jul 90 16:01:00 GMT
References: <132742@<1990Jul26>
Nf-ID: #R:<1990Jul26:132742:inmet:20600056:000:957
Nf-From: inmet.inmet.com!stt    Jul 27 12:01:00 1990
List-Id: <comp.lang.ada>


Re: Implicit array subtype conversion

It turns out that in Ada 83, implicit array subtype conversion
(aka "sliding") only takes place on array assignment,
and array object initialization at declaration (see RM 5.2.1 and 3.2.1:16).
It is easy to argue that sliding should be applicable in
more circumstances (or less, if it makes no sense for the array type),
but alas, the presence of sliding has been linked to the
use of named-with-others array aggregates (see RM 4.3.1:6).
Generally, where sliding is legal, named-with-others is illegal.

Actually, it is quite possible to imagine a rule that would allow
both to be legal in the same context, by simply stating that
an array aggregate with an OTHERS choice always takes the
bounds implied by the "applicable index constraint" even though
sliding might have allowed for different bounds in the same context.

Ada 9X will likely address this issue.

S. Tucker Taft
Intermetrics, Inc.
Cambridge, MA  02138