using System;

​

class Parent {

    protected bool InternalField { get; set; } = false;

    public Parent() => Say();

    public virtual void Say() => Console.WriteLine($"Parent :: Say {InternalField}");

}

​

class Child : Parent {

    public Child() => InternalField = true;

    public override void Say() => Console.WriteLine($"Child :: Say {InternalField}");

}

public class Program {

    public static void Main() {

        var parent = new Parent();

        var child = new Child();

    }

}