[Vala] Ducktyped foreach

[Philip Van Hoof <spam pvanhoof be>]

In .NET you have Ducktyped foreach stuff. This means that you don't need
to implement IEnumerable to be usable with foreach statements:


public class MyCollection  {
   int[] items;
   public MyCollection() {
      items = new int[5] {12, 44, 33, 2, 50};
   }
   public MyEnumerator GetEnumerator() {
      return new MyEnumerator(this);
   }
   public class MyEnumerator 
   {
      int nIndex;
      MyCollection collection;
      public MyEnumerator(MyCollection coll) {
         collection = coll;
         nIndex = -1;
      }
      public bool MoveNext() {
         nIndex++;
         return(nIndex < collection.items.GetLength(0));
      }
      public int Current  {
         get { return(collection.items[nIndex]); }
      }
   }
}
public class MainClass  {
   public static void Main() {
      MyCollection col = new MyCollection();
      Console.WriteLine("Values in the collection are:");
      foreach (int i in col) 
         Console.WriteLine(i);
   }
}

I figured that we can have this in Vala too. The instance being iterated
must only have the possibility to return an iterator. Although a
Gee.Iteratable ensures this in a type safe way, any instance with a
get_iterator method should be usable for the vala.ForeachStatement

This might make it possible to have funny types that are not really
iteratable yet can provide a get_iterator. For example non-list types
that still allow a foreach:

Person p = ..
foreach (Arm a in p) {
        a.Wave ();
}

The added benefit for this type is that if we ever inherit a type from
Person, say a PersonWithFiveArms then that inherited version must just
override the get_iterator, yet don't become "like a list type".

It's probably too rare indeed, but experimenting with Jürg's excellent
Vala code is too fun, sorry.

Here's a first pseudo-code-something patch that I need to convert to
something that would compile and work.

Am I looking in the right direction for this? Else just put on me on the
right track on IRC or something, or reply here :)


-- 
Philip Van Hoof, software developer
home: me at pvanhoof dot be 
gnome: pvanhoof at gnome dot org 
http://www.pvanhoof.be/blog

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