Re: meaning of "current instance"

["Matthew Heaney" <matthew_heaney@acm.org>]

In article <mG%W3.5997$dp.134843@typhoon-sf.snfc21.pbi.net> , 
tmoran@bix.com  wrote:

>   Is it legal, or is it not?

It doesn't matter if it's legal.  Don't do it.


> The only mention of "current instance"
> of a type that I see in the LRM index is to 8.6(17), which leaves me
> guessing that the usual elaboration order rules apply, even though
> things can be written that are normally un-writeable.

See 3.10.2 (24).


>   If the order of components in a record declaration is changed, it
> usually doesn't break things, or at least the compiler will point out
> that you are using something before it exists.  A usage of "current
> instance" presumably is a red flag to a maintenance programmer that
> re-ordering is treading on thin ice.

No.  Using the "current instance" of the type is *very* common.  It's
how we implement multiple inheritance in Ada95:

  type Digital_Clock (Timer : access Timer_Type) is
    new Limited_Controlled with record
      Hour_Observer : Hour_Observer_Type (Digital_Clock'Access);
      Min_Observer  : Min_Observer_Type (Digital_Clock'Access);
      Sec_Observer  : Sec_Observer_Type (Digital_Clock'Access);
    end record;


(Type Digital_Clock effectively has 4 parent types.)



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