Is "Protocol Inheritance" the same thing as "Protocols conforming to Protocols"

[xwu (Xiaodi Wu)]

@DandyLyons

But I'm confused. I'm not even trying to conform a protocol to a protocol. I'm trying to make protocol Category inherit from Hashable . Is that the same thing as conforming a protocol to a protocol ? Why doesn't this protocol want to inherit?

To clarify, there are two things that look the same: the protocol Category and the existential type (also called protocol type) Category. Even though they look the same, they are actually two different things. When you use a protocol as a type, you are using the existential type. That existential type cannot conform to any protocols, even itself (i.e., Category does not conform to Category).

For more information, see the corresponding educational note for this topic.

@xAlien95

If there was an explicit way to refer to existential protocol types, e.g. using any Category , you would be able to explicitly add conformances.

That is not quite correct. Even if we change the spelling of existential types, it does not mean that you can conform such types to protocols; and even if we implement a feature permitting users manually to state such conformances, it does not mean that it is possible (in fact, it is impossible) to write a conformance that can correctly conform an existential type to any arbitrary protocol. For one example, see the educational note.