Class vs Structure Vs Module in Visual Basic .Net

[TamusJRoyce]

I was quickly curious what the difference between a class, a structure, and a module is in Visual Basic .Net in relation to C++.

Is a Structure truly a struct like in C, or is it essentially a class with all members defaultly public? And what is the point of a Module (I used one back in the day with VB6, but have read they have major speed issues--and why are they inefficient?).

How do these three fit in with each other in relation to Polymorphism? Can I inherit a Module from a Class or vs versa?

I've found it's quite hard to find documentation in MSDN on things like this, and googling hasn't gotten me far. And I hate to start up a new thread on such a fundamental/easy question...

I am basically interested in knowing features one may have over another. And if anyone knows of how to do a Union like in C/C++, I would be greatly appreciative to know how.

Hopefully Helpful,

TamusJRoyce

[balabaster]

A module is the same as a Public Static Class in C# (Public NotInheritable Class in VB). Cosmetically you don't have to specify the class name to reference its methods like you do with a Public Static Class. In a module, members by default are public and as such a variable can be seen across the global scope of your application. In a class you normally have to reference variables and other members by the fully qualified path name, i.e. instance.member, however, if you use imports MyNamespace.MyM odule in VB or using MyNamespace.MyC lass in C# then you can access the member directly just as if it were in a module... as long as the member is declared as shared in VB or static within C#.

If you do some digging into the underlying IL, you will see that both modules and static classes are implemented in the same way, so really - modules and static classes are the same, any differences are purely cosmetic.

Of course, there's always some caveats: The keyword Module can only be used directly within a namespace, you cannot nest modules... however, you can nest static/notinheritable classes. So while under the covers they're the same, syntactically, one is not allowed.

A module cannot inherit or implement anything... it can contain subclasses


At first glance a structure is similar to a class in many ways, one noticeable way that it's different is that it's passed ByVal instead of ByRef between methods - unless you explicitly state that it must be passed ByRef. Structs perform better due to heap/stack management differences because structs are stored on the stack whereas classes are stored on a heap. When a struct stores small amounts of data, it is stored in memory more efficiently than a class.