Classes Vs Modules

Both classes and modules are reference types that encapsulate items defined within, but they differ in how these items are accessed from other procedures.

The primary difference between classes and modules is that classes can be instantiated and standard modules cannot. Because there is never more than one copy of a standard module's data, when one part of your program changes a public variable in a standard module, any other part of the program gets the same value if it subsequently reads that variable. Class data, on the other hand, exists separately for each instantiated object. Another difference is that unlike standard modules, classes can implement interfaces.

Classes and modules also employ different scope for their members. Members defined within a class are scoped within a specific instance of the class, and exist only for the lifetime of the object. The practical result is that, to access class members from outside a class, you must use only fully qualified names; for example, Object.Member. Members declared within a standard module, on the other hand, are shared by default, and are scoped to the declaration space of the standard module's containing namespace. This means that public variables in a standard module are effectively global variables because they are visible from anywhere in your project, and they exist for the life of the program. Unlike class members, members of standard modules are implicitly shared and cannot use the Shared keyword.