Why is GUID attribute needed in the first place?

Question

What is the necessity for the GUID attribute? why don\'t just let the compiler handle this automatically?!

Answer 1

To read this definition you would need to look up the meaning of each of those attributes. The first, ComVisibleAttribute, is described as this:

Controls accessibility of an individual managed type or member, or of all types within an assembly, to COM.

That tells us that ComVisible is something to do with COM, and lets us specify whether a particular type is visible to COM programs. Further down on the page is a link to more details on what the attribute is for and how its used by the type library exporter.

The second, GuidAttribute, is a bit less helpful at first:

Supplies an explicit System.Guid when an automatic GUID is undesirable

but again, you have to read the rest of the way down, and you will see another mention of the type library exporter.

Putting these two together, it starts to become clear that these two attributes control how IEnumerator is processed when exported to a type library. If you don't know what a type library is, this will probably not mean much to you. If you are not using COM interop, then those attributes can safely be ignored. If you are using COM interop, you would need to know the Guid to properly access the interface from unmanaged COM code.

Microsoft puts these on every interface definition in case you need them; part of the skill in reading the MSDN pages is to recognize this type of information and know when it isn't any use to you. Now that you know what those two attributes are for, you should be able to figure out if they are relevant to you, and ignore them otherwise.