我有一个泛型类，我希望能够与默认类型一起使用.现在我可以用任何类型初始化它，但我必须是显式的.
//Initialize with a type
MyManager<MyCustomerObject>()
// Initialize with NSObject (what I want to be my default type)
MyManager<NSObject>()
// This doesn't work, but I want this kind of functionality
class MyManager<T = NSObject> {}
// So I can create my manager like so and it inserts the default type as NSObject
MyManager() //Or MyManager<>()
这在Swift 有可能吗？
不支持默认的泛型参数，但可以通过在受类型约束的扩展上定义默认的init()来伪造它，在这种情况下，编译器将足够聪明地使用该类型.例如.:
class MyManager<T> {
let instance: T
init(instance: T) {
self.instance = instance
}
}
extension MyManager where T == NSObject {
convenience init() {
self.init(instance: NSObject())
}
}
现在您可以不带参数地初始化类型，它将默认为MyManager<NSObject>:
let mm1 = MyManager(instance: "Foo") // MyManager<String>
let mm2 = MyManager(instance: 1) // MyManager<Int>
let mm3 = MyManager() // MyManager<NSObject>
SwiftUI经常使用这种技术.