C# 4 Covariant & Contravariant

C#4封閉的泛型支援Covariant & Contravariant,例如以下程式在C# 3不可編譯;在C# 4可正常執行

1 class outputsafe

2 {

3 static void Main(string[] args)

4 {

5 IEnumerable<string> data = new string[] { "a", "b" };

6 PrintData(data);

7 }

8 public static void PrintData(IEnumerable<object> o)

9 {

10 foreach (var t in o)

11 {

12 Console.WriteLine(t);

13 }

14 }

15 }