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From: "Nick Roberts" <Nick.Roberts@dial.pipex.com>
Subject: Re: Any research putting c above ada?
Date: 1997/04/20
Message-ID: <01bc4da6$70afa380$f4f582c1@xhv46.dial.pipex.com>#1/1
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Organization: UUNet PIPEX server (post doesn't reflect views of UUNet PIPEX)
Newsgroups: comp.lang.ada
Date: 1997-04-20T00:00:00+00:00
List-Id: <comp.lang.ada>



In answer to the questions about putting different fruits in the same
array, have a gander at this:

-----------
type Kind_Of_Fruit = (Apple, Orange, {other kinds});

type Fruit_Descriptor(Kind: Kind_Of_Fruit) is
   record
      case Kind is
         when Apple =>
            AV: Apple_Variety;
            {other components}
         when Orange =>
            OV: Orange_Variety;
            {other components}
         {etc for other kinds}
      end case;
   end record;

type Fruit_Reference is access Fruit_Descriptor;

...

FA: array (Location_In_Bowl) of Fruit_Descriptor;

...

begin
   FA(1) := new Fruit_Descriptor'(Apple,Golden_Delicious,...);
   FA(2) := new Fruit_Descriptor'(Orange,Satsuma,...);
   ...
end;

------------
Thus one might (want to) have different fruits in the same array.

The above can be done in C++ using classes, but in order to get the
equivalent of Ada's automatic deallocation, the appropriate destructor has
to be declared. This is not difficult, but it's easier (and less
error-prone) in Ada.

To do this in C is not directly possible. The deallocation has to be done
specifically, and the correct size has to be specified when allocating each
fruit (since the size of an apple descriptor may be different to that of an
orange, and other fruits). In addition, nothing prevents apple data and
orange data being mixed up accidentally (lint can only check static
contraventions). This is really a pain, and illustrates how C is not very
suitable for large-scale software.

Nick.