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Newsgroups: comp.lang.ada
Date: Thu, 21 May 2020 07:20:15 -0700 (PDT)
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Subject: Re: Q: How to inherit methods from parent tagged object?
From: Warren <ve3wwg@gmail.com>
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Xref: reader01.eternal-september.org comp.lang.ada:58755
Date: 2020-05-21T07:20:15-07:00
List-Id: <comp.lang.ada>

On Thursday, 21 May 2020 09:50:24 UTC-4, Jere  wrote:
> On Thursday, May 21, 2020 at 9:23:52 AM UTC-4, Warren wrote:
> > I've become rusty and am refreshing myself with Ada again using a pet project..
> > 
> > I have a tagged class that I want to inherit all but one of the methods for:
> > 
> >    type Flash is new Emulator.Memory.Flash with private;
> >    
> >    procedure Initialize(Obj: in out Flash);
> > --   function Fetch(Obj: in out Flash; Address: Address_Type) return Word_Type;
> > --   function First_Address(Obj: in Flash) return Address_Type;
> > --   function Last_Address(Obj: in Flash) return Address_Type;
> > 
> > The only thing I want to override in the new object is the Initialize procedure for the new object. There must be a way to specify that but I can't seem to goggle it on the interwebs. Every example I can find completely redefines all of the methods.  
> > 
> > I'd like to avoid re-specifying the bodies of Fetch, First_Address and Last_Address for the new object, if that is permitted.  If memory serves, there is a way... but the worms have invaded my brain.
> 
> I feel like you are either leaving out some other info about
> Emulator.Memory.Flash or I am just completely misunderstanding.
> If you only want to override Initialize, then just do that:
> 
>    type Flash is new Emulator.Memory.Flash with private;
>    overriding procedure Initialize(Obj: in out Flash);
> 
> The "overriding" keyword is optional but good practice.  Doing this
> will override Initialize but not the other operations.  If this
> doesn't work you need to tell us more about any errors you are
> encountering.  Note that this is true for almost all languages
> that support inheritance, you just override the operations you want 
> to and the rest will just use the baseclass version.

When I just try to override Initialize, I get the error:

emulator-memory-attiny13.ads:46:09: missing full declaration for private extension

Arrrg, I found the problem.. and am embarrassed to say, I was missing the:

  type Flash is new Emulator.Memory.Flash with null record;

in the private section. DOH!

Thanks for your time.