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From: dewar@merv.cs.nyu.edu (Robert Dewar)
Subject: Re: [Q] : Unchecked conversion
Date: 1996/11/09
Message-ID: <dewar.847574078@merv>#1/1
X-Deja-AN: 195564261
references: <01bbce46$0f818680$829d6482@joy.ericsson.se>
organization: New York University
newsgroups: comp.lang.ada
Date: 1996-11-09T00:00:00+00:00
List-Id: <comp.lang.ada>


iJonas Nugren asks

"1)  Is this a Gnat(3.04a) imposed limitation on Unchecked_Conversion
     or is my code illegal irregardless of compiler?
"

asking about a case of unchecked conversion between uncosntrained array
types.

In the current version of GNAT, we have relaxed this restrictoin somewhat
and allow the source to be an unconstrained array, but not the target.
Letting the target be an unconstrained array is pretty bogus, where would
the bounds come from in the general case, yes, I guess you could allow
it in limited cases but it seems dubious (note that the DEC Ada 83
compiler has exactly the same set of restrictions -- that was the
inspiration for relaxing the GNAt rules).

You can easily do what you want however, by instantiating UC locally
for a constrained subtype with appropriate bounds. That's really a 
preferable way of doing things in any case.

Or you can do UC between pointers to such unconstrained types (that's
probably all the UC between the arrays does anyway, and that way you
avoid making a copy of the array, converting pointers just gives you
a different view of the data, and is usually preferable).