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From: tmoran@bix.com
Subject: Re: C/C++ programmer giving Ada95 a chance -- writing an emulator.
Date: 2000/03/30
Message-ID: <iRNE4.153$sy6.23019@news.pacbell.net>#1/1
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References: <38E2DC8A.45AE7226@research.canon.com.au>
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Newsgroups: comp.lang.ada
Date: 2000-03-30T00:00:00+00:00
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> Here's one way to use dispatching on tagged types ...
>    Op_Table : array (Opcode) of Op_Root
>     := (Op_Root (O0),
>         Op_Root (O1),
>         Op_Root (O2),
>         Op_Root (O3),
>         others => OU
>         );
>    ...
>       Func (Op_Root'Class (Op_Table (IR)));

> The main loop, on a sparc with gnat 3.12p -gnatp -O3, is 9 instructions
  It also works with Gnat 3.12p NT.  But both ObjectAda and Janus
print a series of "undefined opcode".  It seems to me that is
actually the correct behavior, since Op_Table is a table of Op_Root,
not a table of Op_Root'class.  I'd be inclined to report this as
a Gnat error.
  As alternatives, you might make Op_Table a table of
access-to-Op_Root'class or use a "case statement IR is".
The latter, of course, is explicitly what you were trying to avoid.

> I don't think it is any clearer or better than my original.
  Agreed.  It's slower, more complex, and, it seems to me, has
no benefits.