Linq fast indexOf

IndexOf.cs

namespace System.Linq {
  
  public static class EnumerableExtensions {
  
    public static int IndexOf<T1>(this IEnumerable source, Func<T1, bool> predicate) {
      
      var enumerator = source.GetEnumerator();
      bool lastEval = false;
      int index = -1;
      
      
      while (enumerator.MoveNext() && !(lastEval = predicate(enumerator.Current))) {
        ++index;
      }
      
      //If the last evaluation is still false we broke the loop without finding anything
      return lastEval ? index : -1;
      
    }
    
  }
  
}