Are GUIDs necessary to use interfaces in Delphi?

Question

The official documentation says they are optional. I know COM interop requires a unique identifier for each interface but every interface example I see has a GUID whether it's used with COM or not? Is there any benefit to including a GUID if its not going to be used with COM?

Answer 1

I've noticed that some methods such as Supports (to determine if a class conforms to a specific interface) require that you define a GUID before you can use them.

This page confirms it with the following information:

Note: The SysUtils unit provides an overloaded function called Supports that returns true or false when class types and instances support a particular interface represented by a GUID. The Supports function is used in the manner of the Delphi is and as operators. The significant difference is that the Supports function can take as the right operand either a GUID or an interface type associated with a GUID, whereas is and as take the name of a type. For more information about is and as, see Class References.

Here's some interesting information about interfaces, which states:

Why does an interface need to be uniquely identifiable? The answer is simple: because Delphi classes can implement multiple interfaces. When an application is running, there has to be a mechanism that will get pointer to an appropriate interface from an implementation. The only way to find out if an object implements an interface and to get a pointer to implementation of that interface is through GUIDs.

Emphasis added in both quotes.

Reading this entire article also makes you realize that QueryInterface (which requires a GUID) is used behind the scenes for reasons such as reference counting.