[swift-evolution] [Pitch] Refactor Metatypes
Adrian Zubarev
adrian.zubarev at devandartist.com
Sun Oct 2 06:10:57 CDT 2016
You can read the updated version of the proposal on a sub-branch: https://github.com/DevAndArtist/swift-evolution/blob/refactor_existential_metatypes/proposals/0126-refactor-metatypes.md
--
Adrian Zubarev
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Am 2. Oktober 2016 um 11:47:50, Goffredo Marocchi (panajev at gmail.com) schrieb:
Love it :)!
Sent from my iPhone
On 2 Oct 2016, at 09:37, Adrian Zubarev via swift-evolution <swift-evolution at swift.org> wrote:
That’s right. I was about to say something similar about the Of.
Actually Type<T> would be the correct name for the static/concrete metatype.
We already have this notation but not in a generic way T.Type
If we add of only in our mind to Type<T>, we’ll get “Type of a type T” which is shortly referred as a “metatype of T”. (Array<Element> - Array of Element type)
Since Subtype<T> in reality is some *existential metatype* and the whole talk about existential types now tend to have the Any prefix, lets follow that trend here too.
Type<T> - (static/concrete/exact) metatype.
AnyType<T> - existential metatype.
It might be even easier to memorise this name than Subtype.
The example from the proposal rewritten:
// Types:
protocol Foo {}
protocol Boo : Foo {}
class A : Foo {}
class B : A, Boo {}
struct S : Foo {}
// Metatypes:
let a1: Type<A> = A.self //=> Okay
let p1: Type<Foo> = Foo.self //=> Okay
let p2: Type<Boo> = C.self //=> Error -- `C` is not the same as `Foo`
let any_1: AnyType<Any> = A.self //=> Okay
let any_2: AnyType<Any> = Foo.self //=> Okay
let a_1: AnyType<A> = A.self //=> Okay
let p_1: AnyType<Foo> = A.self //=> Okay
let p_2: AnyType<Foo> = Foo.self //=> Error -- `Type<Foo>` is not a subtype of `AnyType<Foo>`
// Generic functions:
func dynamic<T>(type: AnyType<Any>, `is` _: Type<T>) -> Bool {
return type is AnyType<T>
}
func dynamic<T>(type: AnyType<Any>, `as` _: Type<T>) -> AnyType<T>? {
return type as? AnyType<T>
}
let s1: Type<S> = S.self
dynamic(type: s1, is: Foo.self) //=> true
dynamic(type: s1, as: Foo.self) //=> an `Optional<AnyType<Foo>>`
The type(of:) function could now stay, because now we’d only need to change the return type.
func type<T>(of instance: T) -> AnyType<T>
Isn’t this a good compromise?
--
Adrian Zubarev
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Am 2. Oktober 2016 um 09:01:45, Pyry Jahkola via swift-evolution (swift-evolution at swift.org) schrieb:
OTOH, we don't have ArrayOf<Element> or DictionaryOfKeyAndValue<Key, Value>, while we still pronounce them that way. I don't think prepositions belong in the name of types but in exceptional cases, and this doesn't sound exceptional enough to me.
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