Assume you’d need to create like 5–10 different sub-protocols where each of
them has a unique type. We also let the new protocol unmodified, so that we
only use the where clause from SE–0142 to specify all the associated types.
protocol IntFoo : Foo where Inner = Int {}
StringFoo
DoubleFoo
…
Now for each type we need to repeat the same pattern all over again, just to
specify all the associated types of Foo.
Wouldn’t be handy to have autogenerated GenericFoo<Inner : SomeOtherProtocol> :
Foo which will covert that for you.
The only step you’d need to do is to pass a type you want to the parameter list.
The generics manifesto explains two different features what generic protocols
could do. That is exactly the first feature of these two, where the second
requested feature from the generics manifesto is no go for Swifts generic
system.
--
Adrian Zubarev
Sent with Airmail
Am 3. Dezember 2016 um 20:58:52, Xiaodi Wu ([email protected]) schrieb:
protocol Foo { associatetype Inner : SomeOtherProtocol }
// Assuming String and Int conforms to SomeOtherProtocol
protocol StringFoo : Foo where Inner == String {}
protocol IntFoo : Foo where Inner == Int {}
On Sat, Dec 3, 2016 at 13:57 Adrian Zubarev <[email protected]>
wrote:
To which code ‘above’ do you refer exactly?
--
Adrian Zubarev
Sent with Airmail
Am 3. Dezember 2016 um 20:29:05, Xiaodi Wu ([email protected]) schrieb:
On Sat, Dec 3, 2016 at 12:02 PM, Daniel Leping via swift-evolution
<[email protected]> wrote:
@Adrian, my comments inline below. Hope this helps.
On Sat, Dec 3, 2016 at 6:22 PM, Adrian Zubarev
<[email protected]> wrote:
There is one thing that I want to point out with pitched syntactic sugar.
GenericMyProtocolName<U> will also let you reuse T within a generic type, where
currently we cannot nest protocols into types. Even if we could, it’s not clear
if nested declarations like protocol MyTProtocolName : MyProtocolName where U
== T would be possible, so that T from the outer generic type is accessible.
Autogenerating the only possible generic protocols from protocols with
associated types as a syntactic sugar to reduce spawning of types like IntFoo
(as previously showed) seems reasonable to me. It does not break the current
protocol system, but solves the first generic protocol feature from the
generics manifesto.
There are still a few more questioned to answer:
How dow we want the generated parameter list to look like?
The most obvious thing is to do something like Foo<Alias1 = Int, Alias2 =
String>. Otherwise we'll have to add some sort of associatedtype sorting
before; which doesn't sound good and just adds more complexity. Any other
options?
Can we drop Generic prefix without collisions?
I'm pretty sure we could just use existing protocols. All the namings can be
compiler generated as a function from protocol and arguments.
Does this syntactic sugar improves the stdlib or affect ABI?
Don't see any implications. Assuming current stdlib doesn't use the feature.
It's rather an addition than change.
There are probably some more questions I cannot foresee by myself. Feel free to
jump in the discussion. ;)
PS: Yes this syntactic sugar does create an alternative way of creating ‘kinda’
the same protocol twice, but it reuses the pattern more naturally.
protocol Foo { associatetype Inner : SomeOtherProtocol }
// Assuming String and Int conforms to SomeOtherProtocol
protocol StringFoo : Foo where Inner == String {}
protocol IntFoo : Foo where Inner == Int {}
I thought I understood the initial topic of discussion, but I am lost here.
What is unsatisfactory about the code you wrote above and why do we need new
sugar for it?
// VS.
// autogenerated
procotol GenericFoo<Inner : SomeOtherProtocol> : Foo { … }
// usage
GenericFoo<String>
GenericFoo<Int>
// or
typealias StringFoo = GenericFoo<String>
typealias IntFoo = GenericFoo<Int>
// The usage I propose is just do
typealias StringFoo = Foo<Inner = String>
//also in an inheritance like this:
class FooClass : Foo<Inner = String>, Foo<Inner = Int> {
//My question here is, though: how do we access Inner from FooClass
//Like this?
typealias InnerInt = Foo<Inner = String>.Inner
}
--
Adrian Zubarev
Sent with Airmail
Am 3. Dezember 2016 um 16:43:43, Daniel Leping ([email protected])
schrieb:
In general I'm very positive with the idea of generic
protocols. This discussion is more about syntactic sugar, though I
really like where it goes.
Off topic:
IMO, we should revisit approaches others already use for conflicts
resolution. I personally tend to get something similar to Scala
traits. Should fit POT smoothly and naturally.
On Sat, 3 Dec 2016 at 16:30 Adrian Zubarev <[email protected]>
wrote:
If I’m not mistaken here, extension Foo where T == Int will have an error of
redeclaration foo anyways.
--
Adrian Zubarev
Sent with Airmail
Am 3. Dezember 2016 um 15:22:56, Adrian Zubarev
([email protected]) schrieb:
extension Foo where T == Int {
func foo() {
self.bar(o: 42) // calls a function that accepts an Int
}
}
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