How to simulate multiple inheritance without interfaces?

Like Marcus said using interface + extension methods to make something like mixins is probably your best bet currently.

also see: Create Mixins with Interfaces and Extension Methods by Bill Wagner Example:

using System;

public interface ISwimmer{
}

public interface IMammal{
}

class Dolphin: ISwimmer, IMammal{
        public static void Main(){
        test();
                }
            public static void test(){
            var Cassie = new Dolphin();
                Cassie.swim();
            Cassie.giveLiveBirth();
                }
}

public static class Swimmer{
            public static void swim(this ISwimmer a){
            Console.WriteLine("splashy,splashy");
                }
}

public static class Mammal{
            public static void giveLiveBirth(this IMammal a){

        Console.WriteLine("Not an easy Job");
            }

}

prints splasshy,splashy Not an easy Job

Multiple inheritance in a form of a class is not possible, but they may be implemented in multi-level inheritance like:

public class Base {}

public class SomeInheritance : Base {}

public class SomeMoreInheritance : SomeInheritance {}

public class Inheriting3 : SomeModeInheritance {}

As you can see the last class inherits functionality of all three classes:

• Base,
• SomeInheritance and
• SomeMoreInheritance

But this is just inheritance and doing it this way is not good design and just a workaround. Interfaces are of course the preferred way of multiple inherited implementation declaration (not inheritance, since there's no functionality).

Although not quite multiple inheritance, you can get "sort of mixin functionality" by combining interfaces with extension methods.

As C# only supports single inheritance, I believe you'll need to add more classes.

Are there specific reasons for not using interfaces? It's not clear from your description why interfaces are not suitable.