Visual Basic includes five operators that return results based on an operand's object properties.
Is
The Is operator determines whether two object reference variables refer to the same object instance.
result = object1 Is object2
If both object1 and object2 refer to the same object instance, the result is true; otherwise, the result is False. You can also use the Is operator to determine if an object variable refers to a valid object. This is done by comparing the object variable to the Nothing keyword:
If (customerRecord Is Nothing) Then
The result is true if the object variable does not hold a reference to any object.
IsNot
New in 2005. The IsNot operator is equivalent to the Is operator used with the Not logical operator. The statement:
If (customerRecord IsNot Nothing) Then
is the same as:
If Not (customerRecord Is Nothing) Then
There is no functional difference between the two statements. The IsNot operator was added to VB to make such statements more readable.
TypeOf
The TypeOf operator determines if an object variable is of a specific data type. It is always used with the Is operator. (It does not work with the new VB 2005 IsNot operator.) The following statement tests an object variable to see if it is an Integer.
If (TypeOf someNumber Is Integer) Then
AddressOf
The AddressOf operator returns a procedure delegate that can be used to reference a procedure through a variable. In VB¬6, the AddressOf operator returned a function pointer, the memory address of the function. While the .NET version of this operator serves a similar purpose, it does not return a memory address. The .NET Framework reserves the right to move objects (including procedures) to new memory locations at any time, so you cannot depend on the memory address.
For details on the AddressOf operator, including usage information, see the AddressOf Operator entry in Chapter 12.
GetType
The GetType operator returns a System.Type object that contains information about the data type of the operand. You cannot use expressions or variables as operands; you must pass a data type itself. You can use VB data types (like Integer or String), .NET core types (like System.Int32), or the name of any class, structure, or similar construct. For example:
result = GetType(Integer)
returns a System.Type object that provides information about the System.Int32 data type, which is the true data type of the Visual Basic Integer data type.
