[英]Issue with protocol conformance in Swift using associatedtype
我不能使類符合使用associatedtype
協議。 在Playground中,我輸入了一個簡短而簡單的示例來顯示該問題:生成ItemType
兼容項的生產者和使用它們的消費者。 它跟隨:
protocol ItemType { }
protocol Producer: class {
associatedtype T: ItemType
func registerConsumer<C: Consumer where C.T == T>(consumer: C)
}
protocol Consumer: class {
associatedtype T: ItemType
func consume<P: Producer where P.T == T>(producer: P, item: T)
}
struct EmptyItem: ItemType { }
class DummyProducer: Producer {
var consumer: DummyConsumer?
func registerConsumer(consumer: DummyConsumer) {
self.consumer = consumer
}
}
class DummyConsumer: Consumer {
func consume(producer: DummyProducer, item: EmptyItem) {
print("Received \(item) from producer \(producer)")
}
}
Xcode警告我以下錯誤:
Playground execution failed: MyPlaygroundYeYe.playground:14:7: error: type 'DummyProducer' does not conform to protocol 'Producer'
class DummyProducer: Producer {
^
MyPlaygroundYeYe.playground:3:20: note: protocol requires nested type 'T'
associatedtype T: ItemType
^
MyPlaygroundYeYe.playground:22:7: error: type 'DummyConsumer' does not conform to protocol 'Consumer'
class DummyConsumer: Consumer {
^
MyPlaygroundYeYe.playground:9:10: note: protocol requires function 'consume(_:item:)' with type '<P> (P, item: EmptyItem) -> ()' (aka '<τ_1_0> (τ_1_0, item: EmptyItem) -> ()')
func consume<P: Producer where P.T == T>(producer: P, item: T)
^
MyPlaygroundYeYe.playground:23:10: note: candidate has non-matching type '(DummyProducer, item: EmptyItem) -> ()' [with T = EmptyItem]
func consume(producer: DummyProducer, item: EmptyItem) {
^
關於該問題的解決方案(如果存在)的任何建議?
你應該像這樣定義你的DummyProducer
和DummyConsumer
類:
class DummyProducer: Producer {
typealias T = EmptyItem
func registerConsumer<C: Consumer where C.T == T>(consumer: C) {
}
}
class DummyConsumer: Consumer {
typealias T = EmptyItem
func consume<P: Producer where P.T == T>(producer: P, item: T) {
}
}
由於您在協議定義中嚴格指定了associatedType
T
為ItemType
,因此您無法在類中僅使用EmptyItem
,因為EmptyItem
不是唯一可以采用ItemType
協議的結構。
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