Re: Full view of a private partial view cannot be a subtype

[Jere <jhb.chat@gmail.com>]

On Sunday, December 3, 2017 at 7:01:50 AM UTC-5, Jeffrey R. Carter wrote:
> 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.

Yes.  Sorry about that.  In my haste to covert what I had to a reduced example
I forgot to make it null in the visible part.  I would normally only hide that
for private types.

> 
> > 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.

I thought I remembered reading in the RM somewhere that if a renaming was a
completion, that it was equivalent to a wrapper, but to be honest my memory
isn't great.  And even if I remembered correctly, I may not have understood
the context of that fully.


> 
> > 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.
> 
Thanks!  I didn't even think about nesting it like that.  That'll work.