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Newsgroups: comp.lang.ada
Date: Sat, 2 Jun 2018 08:55:05 -0700 (PDT)
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Subject: Re: Using interfaces
From: Jere <jhb.chat@gmail.com>
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Xref: reader02.eternal-september.org comp.lang.ada:52857
Date: 2018-06-02T08:55:05-07:00
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On Saturday, June 2, 2018 at 11:20:53 AM UTC-4, gautier...@hotmail.com wrote:
> Hello,
> I am developing a package for displaying some kinds of figures on an open set of devices. I'm trying to use interfaces for that. 
> 
> SNIPPED...
>
> this is okay but I would need to copy-paste the same implementation code of Filled_Rectangle for device X in the case of Figure_B and so on. Not nice!
> 
> How do I get something like Figure_A_on_Device_X ?
> Am I expecting too much from interfaces?
> 

I generally do something similar to what you do in Rust:

      type Figure_A_on_Device_X is new Figure_A and Any_Device with record
         Device_Impl : Device_X;
      end record;
      procedure Filled_Rectangle (device: Figure_A_on_Device_X);

and then

      procedure Filled_Rectangle (device: Figure_A_on_Device_X) is
      begin
         device.Device_Impl.Filled_Rectangle;
      end Filled_Rectangle;

You can also make Figure_A_on_Device_X a private type to hide that.