Why is it possible for Error protocol? For any other protocol, we receive error
protocol SomeProtocol {
}
struct Test1<T> where T: SomeProtocol {
}
struct Test2<T> where T: Error {
}
let test1: Test1<SomeProtocol> = Test1() ----> Protocol 'SomeProtocol' as a type cannot conform to the protocol itself
let test2: Test2<Error> = Test2() ----> It's Ok
CodePudding user response：
This is just an exception in the rule. It is documented here:
Exceptions
When used as a type, the Swift protocol
Errorconforms to itself;@objcprotocols with no static requirements can also be used as types that conform to themselves.
If it weren't for this exception, you wouldn't be able to do Result<T, Error> or AnyPublisher<T, Error> to say "some result that can be any error" or "a publisher that can emit any error".