C#'s Greatest Mistakes

C# is a lovely language in many ways... but it's not perfect. Mistakes made early in a language or platform's development are often impossible to fix afterwards, so this talk isn't a set of suggestions for the C# team. Instead it's a reflection on what we might do if we had a time machine. Which features which seemed like a good idea at the time have actually caused the development community hours of frustration? Which choices have caused confusion? What could we do differently next time?