Question

I have the following base and derived (partial, for sake of brevity) classes:

class Base {
     public abstract int[] someArray { get; }
}

class Derived : Base {
     private readonly static int[] _someArray = new int[] { 1,2,3,4 };
     public override int[] someArray { 
         get {
              return _someArray;
         }
     }
}

What I would like now, is put the new int[] { 1,2,3,4 } in the return part of the getter. But, that would create a new array every time the getter is called.

Is it possible to directly return some kind of object, which stays the same for all objects of class Derived ?

Something along the lines of (I know this is invalid C#):

  get {
        return (int[]) { 1, 2, 3, 4 };
  }

Answer 1

If you only want to put the new int[] { 1,2,3,4 } part into the getter, that’s easy…

 private static int[] _someArray = null;
 public override int[] someArray { 
     get {
          return _someArray ?? (_someArray = new int[] { 1,2,3,4 });
     }
 }

You’d lose the readonly then, though.

UPDATE: Generics solution

Or you could abuse the features of generics for that:

// Of course you still want to use the non-generic class Base
abstract class Base {
    public abstract int[] someArray { get; }
}

abstract class Base<T> : Base where T: Base<T> {
     // Will be created once for every T, i.e. every derived class.
     private static int[] _someArray;

     public override int[] someArray {
        get { return _someArray ?? (_someArray = CreateArray()); }
     }

     protected abstract int[] CreateArray();
}

sealed class Derived : Base<Derived> {
     protected sealed override int[] CreateArray() { 
         return new int[] { 1,2,3,4 };
     }
}

sealed class DerivedB : Base<DerivedB> {
    protected sealed override int[] CreateArray() {
        return new int[] { 2,3,4,5 };
    }
}

Note that this only works for one inheritance level, so i sealed some stuff 🙂