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Newsgroups: comp.lang.ada
Date: Mon, 25 Jan 2021 09:51:37 -0800 (PST)
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Subject: Re: Simple example on interfaces
From: Mario Blunk <marioblunk.alere@gmail.com>
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> You must define "property." What is it? 
With "property" I mean the selectors like p0, p1 or p2.
> In your code these types have p2 
> already. Is this static polymorphism not enough? 
It seems so. Suppose there would be more types like C1, D1, ..., each of which derived from type_base, then
I don't want to define p2 over and over.

> Do you need A2 and B1 
> in a class having p2, with polymorphic objects of the class? Then that 
> would indeed be an interface. 
How would that look like ?

> Now, there is no full multiple inheritance in Ada, if p2 must be a 
> component, you are out of luck. You have only one shot and you have 
> spent it on p0 in the type Base. 
That is forbidden as far as the final application is concerned. The example I posted here is a simplification of a more complex scenario.

> But if p2 could be a function or a getter/setter pair then you can do this: 
> 
> type P2_Interface is interface; 
> function P2 (Object : P2_Interface) return Enum is abstract; 
> 
> type A2 is new A1 and P2_Interface with private; 
> overriding function P2 (Object : A2) return Enum; 
> 
> type B1 is new Base and P2_Interface with private; 
> overriding function P2 (Object : B1) return Enum; 
I need to digest that... I know an interface can not have a selector, just abstract functions.
 
> (I removed annoying "type_" prefix from all types) 
I got used to this notation in order to avoid confusion between a type and a variable. Not important here.