> No, class would not need to be final to conform to a requirement
returning #Self. The difference is that with Self covaries and #Self does
not. This means you *do not need* to guarantee that all subclasses
override a requirement that returns #Self, while you do need to guarantee
that all subclasses override a requirement that returns Self.
I'm probably slow these day, but I(and probably someone else) just can't
understand this. Thank you for your patience in explaining this:
Just after you conforms *base* class to *any* protocol, any possible
subclass *must* (you *have to* guarantee this) conform the same protocol.
class A {..}
class B:A {..}
class C:A {..}
protocol D {..}
extension A: D {}
-> now B&C and any other existed and *possible* subclass *must* conforms to
the same protocol D just because of inheritance. As soon as they are
subclass of A, they *must* be `is D` and *must* have the methods that
return #Self. No?
On 10.05.2016 22:04, Matthew Johnson wrote:
On May 10, 2016, at 1:38 PM, Vladimir.S <sva...@gmail.com> wrote:
On 10.05.2016 20:50, Matthew Johnson wrote:
No, the whole point is that D.f() returns C because C is the requirement
of 'f' is declared to return #Self which is C where the protocol
conformance is declared and implemented. If you want a covariant
requirement you would use Self as the return type, not #Self.
I just followed your example with NSURL.. Probably I don't understand the point,
but you said you want to conform a non-final class to protocol with method ->
#Self.
---------------------<
protocol A { static func createWithString(s: String) -> Self }
extension NSURL: A { // cannot conform because NSURL is non-final }
If we could define a protocol requirement that didn't covary (using
#Self or whatever) we would be able to write the desired conformance.
---------------------<
And I don't understand how do you want to achieve the target, as even if we
'invent' #Self, this (as I understand) can't work as class is not final. Just
like with 'simple' Self - class must be final to conform. Thank you for
clarification.
No, class would not need to be final to conform to a requirement returning
#Self. The difference is that with Self covaries and #Self does not. This
means you do not need to guarantee that all subclasses override a requirement
that returns #Self, while you do need to guarantee that all subclasses override
a requirement that returns Self.
The requirement to guarantee that all subclasses provide this override is the
reason you cannot declare conformance in the case of requirements returning
Self. Since this isn’t necessary for #Self (will probably have a different
name) the class does not need to be final in order to conform.
-Matthew
.
_______________________________________________
swift-evolution mailing list
swift-evolution@swift.org
https://lists.swift.org/mailman/listinfo/swift-evolution
