mcs/tests/gtest-134.cs

   1 // sestoft@dina.kvl.dk * 2004-08
   2
   3 using System;
   4
   5 class MyTest {
   6   public static void Main(String[] args) {
   7     Foo<int?> fni1 = new Foo<int?>(null);
   8     Console.WriteLine(fni1.Fmt());
   9     Foo<int?> fni2 = new Foo<int?>(17);
  10     Console.WriteLine(fni2.Fmt());
  11     Foo<int> fi = new Foo<int>(7);
  12     Console.WriteLine(fi.Fmt());
  13     Foo<String> fs1 = new Foo<String>(null);
  14     Console.WriteLine(fs1.Fmt());
  15     Foo<String> fs2 = new Foo<String>("haha");
  16     Console.WriteLine(fs2.Fmt());
  17   }
  18 }
  19
  20 class Foo<T> {
  21   T x;
  22   public Foo(T x) {
  23     this.x = x;
  24   }
  25
  26   // This shows how to deal with tests for null in a generic setting
  27   // where null may mean both `null reference' and `null value of a
  28   // nullable type'.  Namely, the test (x == null) will always be
  29   // false if the generic type parameter t is instantiated with a
  30   // nullable type.  Reason: the null literal will be considered a
  31   // null reference and x will be boxed if a value type, and hence the
  32   // comparison will be false...
  33
  34   public String Fmt() {
  35     if (x != null)
  36       return x.ToString();
  37     else
  38       return "null";
  39   }
  40 }