using System;

public class Program

{

    public static void Main()

    {

        var a = new ChildA();

        a.SomeMethod();

        var b = new ChildB();

        b.SomeMethod();

        var c = new ChildC();

        // c.SomeMethod(); Doesn't have SomeMethod

    }

}

​

public class ParentClass {}

​

public class ChildA : ParentClass, IHavingSomeMethod

{

   private readonly IHavingSomeMethod _sms;

   public ChildA()

   {

       _sms = new HavingSomeMethodService(); // Have it injected instead!

   }

   public void SomeMethod() => _sms.SomeMethod();

}

​

public class ChildB : ParentClass, IHavingSomeMethod

{

   private readonly IHavingSomeMethod _sms;

   public ChildB()

   {

       _sms = new HavingSomeMethodService(); // Have it injected instead!

   }

   public void SomeMethod() => _sms.SomeMethod();

}

​

public class ChildC : ParentClass

{}

​

public interface IHavingSomeMethod

{

    void SomeMethod();

}

​

public class HavingSomeMethodService: IHavingSomeMethod

{

   public void SomeMethod(){

      Console.WriteLine("SomeMethod");

   }

}