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From: "Randy Brukardt" <randy@rrsoftware.com>
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Subject: Re: new revision ada (exception handling)
Date: Thu, 24 Jun 2004 16:13:58 -0500
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Date: 2004-06-24T16:13:58-05:00
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"Martin Krischik" <krischik@users.sourceforge.net> wrote in message
news:1602287.U74iaLRb4H@linux1.krischik.com...
> Randy Brukardt wrote:
...
> > We considered it briefly, but there are a number of problems with such a
> > feature. (One example is that Text_IO.Enumeration_IO depends on 'Image.
> > How will it know what syntax to read for a user-defined image.) Anyway,
we
> > dropped the idea.
>
> At least for the first question I know the answer. It is the same as for
> 'Output:

No, that's *not* the question. (That's another question, which also needs to
be answered.)

The issue is that Enumeration_IO.Get needs to know the syntax of a
enumeration literal in order to know when to stop reading. For instance, if
a file has:

Red;Green Blue

and you do a Get, the next character to be read is ';', and "Red" will be
passed to 'Image.

But if you allow a user-defined 'Image, you don't know what to read in order
to pass it to 'Image. Perhaps the semicolon is part of the literal, perhaps
it is not. Perhaps the case matters to the literal, and perhaps not. So
where does reading stop? (And remember, whatever is done has to be
compatible with existing code and files.)

If you just say that the syntax is still that of an identifier, then what
you can do with a user-defined 'Image is very limited. "Real-Time" and "62B"
would not be legitimate uses of 'Image, and the errors that would occur when
trying to read them would be very mysterious to programmers.

                               Randy.