Iterators and Nullable Types - Mixing nullable and nonnullable operators

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You can mix and match nullable and nonnullable types (this works because there is an implicit conversion from T to T?):

T to T? ):You can mix and match nullable and nonnullable types (this works because there is an implicit conversion from T to T?):

  int? x = null;
  int y = 2;
  int? z = x + y; // equivalent to x + (int?)y

  // z is null

bool?

When supplied operands of type bool?, the & and | operators treat null as an unknown value. So,null | trueis true, because:

1. If the unknown value is false, the result would be true.
   
2. If the unknown value is true, the result would be true.

Similarly,null & falseis false. This behavior would be familiar to SQL users. The following example enumerates other combinations:

  bool? n = null;
  bool? f = false;
  bool? t = true;
  Console.WriteLine (n | n);   // (null)
  Console.WriteLine (n | f);   // (null)
  Console.WriteLine (n | t);   // True
  Console.WriteLine (n & n);   // (null)
  Console.WriteLine (n & f);   // False
  Console.WriteLine (n & t);   // (null)

Null Coalescing Operator

The ?? operator is the null coalescing operator, and it can be used with both nullable types and reference types. It says “If the operand is nonnull, give it to me; otherwise, give me a default value.” For example:

  int? x = null;
  int y = x ?? 5;     // y is 5

The?? operator is equivalent to callingGetValueOrDefaultwith an explicit default value.

Please check back next week for the continuation of this article.

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