The Visual Basic .NET Programming Language

All fields and methods in a Visual Basic .NET program must be contained within a type. In the examples in previous chapters, the simplest type, a module , was used. Modules are just containers for fields and methods, and unlike types such as classes and structures, they are rarely referred to directly.

Normally, members of a container can only be used by qualifying them with the name of the container. However, because the name of a module is usually not important, the members of a module can be used without qualifying them with the module's name.

Module Test Sub Main() Console.WriteLine(Add(10, 20)) End Sub End Module Module Math Function Add(ByVal x As Integer, ByVal y As Integer) As Integer Return x + y End Function End Module

In this example, the Math module contains a function named Add , which the module Test can call without referring to Math at all. The module name can be omitted even if the name is being qualified with other names .

Module Test Sub Main() Console.WriteLine(Acme.Add(10, 20)) End Sub End Module Namespace Acme Module Math Function Add(ByVal x As Integer, ByVal y As Integer) As Integer Return x + y End Function End Module End Namespace

In this situation, the function Add is qualified by the namespace name Acme , but the module name Math is still omitted.

The one situation in which a module's name should be used is when two modules define members with the same name. For example:

Module Test Sub Main() Console.WriteLine(Add(10, 20)) End Sub End Module Module IntegerMath Function Add(ByVal x As Integer, ByVal y As Integer) As Integer Return x + y End Function End Module Module LongMath Function Add(ByVal x As Long, ByVal y As Long) As Long Return x + y End Function End Module

In this example, the call to Add is ambiguous ”is the code intended to call IntegerMath.Add or LongMath.Add ? It's not clear. To resolve the ambiguity, Add must be qualified with the name of the module that the method wants to call.