Why Enumerable.Cast raises an InvalidCastException?

Question

If I can implicitly cast an integer value to a double, like:

int a = 4;    
double b = a;
// now b holds 4.0

Why can I not do this:

Answer 1

To add to Jon's answer cast is mainly useful for objects that implement IEnumerable but nothing else. Take XmlNodeList for example. If you don't have the luxury of using System.Xml.Linq namespace you can use Cast to write some nice LINQ queries against it.

var result = xmlNodeList
    .Cast()
    .Select(e=> e.GetAttribute("A") + e.GetAttribute("B"))
    .ToArray();