Remarks

A type is said to be nullable if it can be assigned a value or can be assigned null, which means the type has no value whatsoever. By default, all reference types, such as , are nullable, but all value types, such as , are not.

In C# and Visual Basic, you mark a value type as nullable by using the ? notation after the value type. For example, int? in C# or Integer? in Visual Basic declares an integer value type that can be assigned null.

The  structure supports using only a value type as a nullable type because reference types are nullable by design.

The  class provides complementary support for the  structure. The  class supports obtaining the underlying type of a nullable type, and comparison and equality operations on pairs of nullable types whose underlying value type does not support generic comparison and equality operations.