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From: ncohen@watson.ibm.com (Norman H. Cohen)
Subject: Re: type casting tagged types in the wrong direction
Date: 1996/03/28
Message-ID: <4je8f8$174r@watnews1.watson.ibm.com>#1/1
X-Deja-AN: 144676104
distribution: world
references: <3159B860.28A6@csehp3.mdc.com>
organization: IBM T.J. Watson Research Center
reply-to: ncohen@watson.ibm.com
newsgroups: comp.lang.ada
Date: 1996-03-28T00:00:00+00:00
List-Id: <comp.lang.ada>

In article <3159B860.28A6@csehp3.mdc.com>, "James A. Squire"
<m193884@CSEHP3.MDC.COM> writes: 

|> Say I have something like: 
|>
|> type A is tagged
|>   record
|>     X : ABC;
|>     Y : DEF;
|>   end record;
|>
|> type B is new A with
|>   record
|>     W : GHI;
|>   end record;
|>
|> type C is new B with
|>   record
|>     Z : JKL;
|>   end record;
|>
|>
|> OK.  Now, let's say that I forgot which type extends off of which, and I
|> write a statement like this: 
|>
|>   Jim  : C;
|>   Jane : B;
|>   Save : JKL;
|>
|> begin
|>   ...
|>   Jim := C (Jane);
|>   Save := Jim.Z;
|>   ...
|> end;
|>
|> GNAT 3.03 compiles this statement.  Is that really right?  Is Jim.Z
|> defined?

The expression Jim.Z is perfectly legal, but the type conversion C(Jane)
is not.  This should be flagged as a compile-time error, because it does
not satisfy the conditions in either 4.6(22) or 4.6(23).

--
Norman H. Cohen    ncohen@watson.ibm.com