[英]How to conform to a protocol with a generic superscript affordance in Swift?
[英]How to cast generic T to conform to protocol
我需要在类中强制转换通用类型以符合协议。 由于容器类必须序列化,因此无法使用约束。 那么,在我已经知道(我可以检查一下)它符合协议的情况下,如何在这种情况下将T转换为ZNumeric?
//: Playground - noun: a place where people can play
import UIKit
protocol ZNumeric {
}
extension Double: ZNumeric {
}
class GenericClass<T> {
}
class RestrictedGenericClass<T:ZNumeric> {
}
class Container {
required init?<T>(type: T.Type) {
let a = GenericClass<T>()
print(a)
if T.self is ZNumeric.Type {
print("is numeric")
//let b = RestrictedGenericClass<T>() // Will not work obviously
//print(b)
}
}
}
let cDouble = Container(type: Double.self) // if T.self is ZNumeric.Type is true
let cString = Container(type: String.self) // if T.self is ZNumeric.Type is false
因为必须在编译时就知道泛型,所以不能只在运行时检查一致性(我很确定)。 我认为这更像您想要的:
class Container {
required init?<T>(type: T.Type) {
let a = GenericClass<T>()
print(a)
}
required init?<T : ZNumeric>(type: T.Type) {
let a = GenericClass<T>()
print(a)
print("is numeric")
let b = RestrictedGenericClass<T>()
print(b)
}
}
较具体的初始化程序将在编译时选择。
我想你在找这个。
protocol ZNumeric {
}
extension Double: ZNumeric {
}
class GenericClass<T> {
}
class RestrictedGenericClass<T:ZNumeric> {
}
class Container<T> {
required init?(value: T) {
}
convenience init?(_ value: T) {
self.init(value: value)
let a = GenericClass<T>()
print(a)
}
}
extension Container where T: ZNumeric {
convenience init?(_ value: T) {
self.init(value: value)
let b = RestrictedGenericClass<T>() // Will not work obviously
print(b)
}
}
print("test Double")
let cDouble = Container(1.1) // if T.self is ZNumeric.Type is true
print("test String")
let cString = Container("") // if T.self is ZNumeric.Type is false
// test Double
// RestrictedGenericClass<Swift.Double>
// test String
// GenericClass<Swift.String>
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