Hello guys! Does someone know how to make this work?

Question

Server Side Swift Developer (SSSD) - Ukraine 🇺🇦 / russian etc. Vapor and swift for other platforms

ඞ丁二 τ2 🐈🥬🐛

Hello guys! Does someone know how to make this work?

(error in the pic)
Also, is it possible to replace any Hashable to something like type param pack in Swift 5.9?

#it #programming #russian

0

24.09.2023

9 ответов

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Куся 🌿⃤ __UKS

Kirill Titov
afaik KeyPath must always be concrete

Exact?

0

24.09.2023

Kirill Titov

Куся 🌿⃤ __UKS
Exact?

say you have property myArray: Int[] (which conforms to Collection), that doesn't mean you can safely assign a dictionary [String: Float] to it just because the dictionary is also a Collection (yet key path is still KeyPath<MyClass, any Collection>. get the idea?

0

24.09.2023

Maxim Krouk

I guess you can experiment with parameter packs, for example this works import Foundation func hash<T, each P: Hashable>( _ item: T, props: repeat KeyPath<T, each P> ) -> Int { var hasher = Hasher() repeat (hasher.combine(item[keyPath: each props])) return hasher.finalize() } struct Example { var p1 = 0 var p2 = true var p3 = "string" } print( hash(Example(), props: \.p1, \.p2, \.p3), hash(Example(), props: \.p1, \.p2, \.p3), hash(Example(), props: \.p1, \.p2), separator: "\n" ) Output: -4549848955267135610 -4549848955267135610 3558766014151656816

0

24.09.2023

Kirill Titov

Maxim Krouk
I guess you can experiment with parameter packs, f...

try writing to WritableKeyPath with protocol

0

24.09.2023

Maxim Krouk

Kirill Titov
try writing to WritableKeyPath with protocol

Well I guess it might not work, but this will (at least you can declare another overload in isolation from the logic) public struct HashingPath<Root> { @usableFromInline internal let _extract: (Root) -> AnyHashable @inlinable public init<Value: Hashable>(_ path: @escaping (Root) -> Value) { self._extract = { path($0) } } // You can declare more overloads here @inlinable public func extract(from root: Root) -> AnyHashable { return _extract(root) } } public func hash<T>(_ item: T, props: [HashingPath<T>]) -> Int { return props.reduce(into: Hasher()) { hasher, prop in hasher.combine(prop.extract(from: item)) }.finalize() }

0

24.09.2023

Maxim Krouk

Kirill Titov
try writing to WritableKeyPath with protocol

Btw this works with the first implementation struct Example { var string: String = "" var protocolValue: any Hashable = 0 } hash(Example(), props: \.string, { AnyHashable($0.protocolValue) })

0

24.09.2023

Kirill Titov

Maxim Krouk
Btw this works with the first implementation stru...

так, стой, у тебя тип свойства структуры — протокол (ставить туда ты можешь любое значение с этим протоколом). но ты не можешь писать в конкретное значение протокольное значение. WritableKeyPath туда тоже не запишет ничего

0

25.09.2023

Maxim Krouk

Kirill Titov
так, стой, у тебя тип свойства структуры — протоко...

Так изначально проблема не подразумевала запись, но вообще по идее решение со структурой будет нормально работать

0

25.09.2023