Question

I have this base class having the following interface:

abstract class Base
{
  abstract public object Val
  {
    get;
  }
}

For any derived classes, Val‘s value must be specified at object creation time.
The question is: How can I make a derived class do this (hopefully at compile time)?
I tried adding a constructor:

abstract class Base
{
  public Base(object value)
  {
    val = value;
  }

  private object val;

  ...
}

But as you can see then I had to declare a private field to store value in it (because Value is read-only).
The problem arises because I want to add some kind of effect to derived classes using the Decorator/Wrapper pattern introduced in GoF Design Patterns. But because I have declared the field inside Base class, the decorators keep saving a copy of the same data and I end up wasting memory.

Answer 1

Try this instead:

abstract class Base 
{
    public Base(object val)
    {
        this.Val = val;
    }

    public object Val { get; private set; }
}

That way, your derived class doesn’t need its own field:

public class Derived : Base
{
    public Derived(object val) : base(val) { }
}