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From: "Jeffrey R. Carter" <spam.jrcarter.not@spam.not.acm.org>
Newsgroups: comp.lang.ada
Subject: Re: Full view of a private partial view cannot be a subtype
Date: Sun, 3 Dec 2017 13:01:47 +0100
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Xref: reader02.eternal-september.org comp.lang.ada:49327
Date: 2017-12-03T13:01:47+01:00
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On 12/03/2017 03:14 AM, Jere wrote:
> 
>     package New_Type1 is
>        subtype Instance is Base.Instance;
>        procedure Operation(Object : in out Instance);
>     private
>        procedure Operation(Object : in out Instance) renames Base.Operation;

You can make the renaming visible as well. There doesn't seem to be any reason 
to hide the fact that Operation is a renaming of Base.Operation.

> I'm also not
> sure the semantics between the method I wanted and the
> method I had to use are the same (in all situations).

No, with a direct renaming, a call to the renaming is the same as a call to the 
original procedure. With a wrapper around the call to the original procedure, 
you have 2 calls. If you inline the wrapper then they should be equivalent.

> 1.  Is there a way to make the full view of a private type
>      a subtype when the partial view is not a subtype? Or am
>      I forced to derive a new type?

You cannot use a subtype to complete a private type. But you're not forced to 
use a derived type and convert all over the place. Another option is

private
    type T is [tagged] [limited] record
       V : Base.T;
    end record;

and then refer to Object.V with no conversions.

If your private type doesn't need to be tagged, you can also do

private
    type T is array (1 .. 1) of Base.T;

and then refer to Object (1), again with no conversions. Given that the bounds 
are static and you're always going to use a static index, I'd expect the 
indexing to be optimized away.

-- 
Jeff Carter
"So if I understand 'The Matrix Reloaded' correctly, the Matrix is
basically a Microsoft operating system--it runs for a while and
then crashes and reboots. By design, no less. Neo is just a
memory leak that's too hard to fix, so they left him in ... The
users don't complain because they're packed in slush and kept
sedated."
Marin D. Condic
65