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From: "Randy Brukardt" <randy@rrsoftware.com>
Newsgroups: comp.lang.ada
References: <2ifue.819$Z97.597@trndny06>
Subject: Re: Virtual Components in Ada and Ruby
Date: Wed, 29 Jun 2005 23:12:48 -0500
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Date: 2005-06-29T23:12:48-05:00
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"Frank J. Lhota" <NOSPAM.lhota@adarose.com> wrote in message
news:2ifue.819$Z97.597@trndny06...
....
> Looking ahead to Ada 201Z, should there be user-defined virtual record
> components? Currently, a component of a record must always be defined as
> a section of memory in a record. Would it be desirable to also be able
> to define a record component in terms of subprograms for reading and
> writing that component?

I think it would likely be too ambiguous with other possibilities to be very
useful.

Certainly, Ada 200Y has "virtual record components" for reading:

    type Something is tagged record ... end record;
    function Virtual (Obj : in Somthing) return Integer;

    Object : Something;

    if Object.Virtual = 10 then ...

But there doesn't seem to be a practical way to make them writable on the
LHS of an assignment. A procedure call isn't too bad in that case:
    Object.Set_Virtual (To => <args>);

                            Randy.