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From: "Nick Roberts" <nickroberts@blueyonder.co.uk>
Newsgroups: comp.lang.ada
Subject: Re: for x'address or variant
Date: Sun, 20 Apr 2003 17:19:54 +0100
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Date: 2003-04-20T17:19:54+01:00
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"kat-Zygfryd" <6667@wp.pl> wrote in message
news:b7u1jh$p6k$1@news.onet.pl...

> I have a tiny problem, I want to have a structure:

> type P is access X;
> type X is record
>     next: array(1..2) of P;
>     left: P;
>     right: P;
> end record;

> wherein the left component uses next(1)'address
> and right component uses next(2)'address,
> unfortunately "for x'address use" statements are
> not allowed within record declarations, and
> variant records don't allow me to access both
> next and left/right exchangably. do you know a way
> to work this out?

Declare the following:

    type Node;
    type Node_Ref is access Node;
    type Leaf_Direction is (Left, Right);
    type Leaf_Pair is array (Leaf_Direction) of Node_Ref;
    type Node is
        record
            Payload: ...;
            Leaves: Leaf_Pair;
        end record;

Now you can reference, for example, the left leaf an object X1 of type Node
by:

    X1.Leaves(Left).all

You can cycle through all the leaves of X1 by:

    for L in Leaf_Direction loop
        ... X1.Leaves(L).all ...
    end loop;

I hope this solves the problem. Say if it doesn't.

--
Nick Roberts
Jabber: debater@charente.de [ICQ: 159718630]