Why does List.ForEach allow its list to be modified?

Question

If I use:

var strings = new List { \"sample\" };
foreach (string s in strings)
{
  Console.WriteLine(s);
  strings.Add(s + \"!\");
}

Answer 1

We know about this issue, it was an oversight when it was originally written. Unfortunately, we can't change it because it would now prevent this previously working code from running:

        var list = new List();
        list.Add("Foo");
        list.Add("Bar");

        list.ForEach((item) => 
        { 
            if(item=="Foo") 
                list.Remove(item); 
        });

The usefulness of this method itself is questionable as Eric Lippert pointed out, so we didn't include it for .NET for Metro style apps (ie Windows 8 apps).

David Kean (BCL Team)