Re: Simple example on interfaces

["Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>]

On 2021-01-25 17:08, Mario Blunk wrote:
> I'm trying to solve a problem of multiple inheritance. It seems to me that an interface could be the solution although the interface is still a mystery for me.
> 
> This is the example code:
> https://github.com/Blunk-electronic/ada_training/blob/master/src/interfaces_1/interfaces_1.adb
> 
> The problem to solve is:
> Type_A2 and type_B1 shall have the property p2 which is type_enum. The anchestors of type_A2 and type_B1 must not have this property.
> Both type_A2 and type_B1 shall inherit p2 from type_C so that p2 must not be written all over again. Would an interface be the solution ?

You must define "property." What is it? In your code these types have p2 
already. Is this static polymorphism not enough? Do you need A2 and B1 
in a class having p2, with polymorphic objects of the class? Then that 
would indeed be an interface.

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.

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 removed annoying "type_" prefix from all types)

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de