我有一个协议Address，它继承自另一个协议Validator，而Address符合扩展中的Validator要求。
还有另一个协议FromRepresentable，其associatedType（ValueWrapper）要求应为Validator。
现在，如果我尝试将Address用作associatedType，那么它就不会编译。它说，
推断类型＆＃39;地址＆＃39; （通过匹配要求＆＃39; valueForDetail＆＃39;）是 无效：不符合＆＃39;验证者＆＃39;。
这种用法是非法的吗？我们不能使用Address代替Validator，因为所有Addresses都是Validator。
以下是我正在尝试的一段代码。
enum ValidationResult {
case Success
case Failure(String)
}
protocol Validator {
func validate() -> ValidationResult
}
//Address inherits Validator
protocol Address: Validator {
var addressLine1: String {get set}
var city: String {get set}
var country: String {get set}
}
////Fulfill Validator protocol requirements in extension
extension Address {
func validate() -> ValidationResult {
if addressLine1.isEmpty {
return .Failure("Address can not be empty")
}
return .Success
}
}
protocol FormRepresentable {
associatedtype ValueWrapper: Validator
func valueForDetail(valueWrapper: ValueWrapper) -> String
}
// Shipping Address conforming to Address protocol.
// It should also implicitly conform to Validator since
// Address inherits from Validator?
struct ShippingAddress: Address {
var addressLine1 = "CA"
var city = "HYD"
var country = "India"
}
// While compiling, it says:
// Inferred type 'Address' (by matching requirement 'valueForDetail') is invalid: does not conform
// to 'Validator'.
// But Address confroms to Validator.
enum AddressFrom: Int, FormRepresentable {
case Address1
case City
case Country
func valueForDetail(valueWrapper: Address) -> String {
switch self {
case .Address1:
return valueWrapper.addressLine1
case .City:
return valueWrapper.city
case .Country:
return valueWrapper.country
}
}
}
更新：提交bug.
答案 0 :(得分：5)
David has already alluded to的问题是，一旦您将协议的associatedtype约束到特定的（非@objc）协议，您必须使用具体的类型来满足这个要求。
这是因为protocols don't conform to themselves - 因此意味着您无法使用Address来满足符合Validator类型的协议的关联类型要求，因为{{1 不符合Address的类型。
在我演示in my answer here时，请考虑反例：
Validator最简单的解决方案是抛弃protocol Validator {
init()
}
protocol Address : Validator {}
protocol FormRepresentable {
associatedtype ValueWrapper: Validator
}
extension FormRepresentable {
static func foo() {
// if ValueWrapper were allowed to be an Address or Validator,
// what instance should we be constructing here?
// we cannot create an instance of a protocol.
print(ValueWrapper.init())
}
}
// therefore, we cannot say:
enum AddressFrom : FormRepresentable {
typealias ValueWrapper = Address
}
关联类型的Validator协议约束，允许您在方法参数中使用抽象类型。
ValueWrapper的
protocol FormRepresentable {
associatedtype ValueWrapper
func valueForDetail(valueWrapper: ValueWrapper) -> String
}
如果您需要关联的类型约束，并且每个enum AddressFrom : Int, FormRepresentable {
// ...
func valueForDetail(valueWrapper: Address) -> String {
// ...
}
}
实例只需要AddressFrom的单个具体实现作为输入 - 您可以使用泛型来使Address成为使用给定的具体类型的地址初始化，以便在您的方法中使用。
AddressFrom的
protocol FormRepresentable {
associatedtype ValueWrapper : Validator
func valueForDetail(valueWrapper: ValueWrapper) -> String
}
的
enum AddressFrom<T : Address> : Int, FormRepresentable {
// ...
func valueForDetail(valueWrapper: T) -> String {
// ...
}
}
但是，如果您同时需要关联的类型约束和，则每个// replace ShippingAddress with whatever concrete type you want AddressFrom to use
let addressFrom = AddressFrom<ShippingAddress>.Address1
实例必须能够处理任何类型的AddressFrom的输入 - 您将会这样做使用类型擦除以便在具体类型中包含任意Address。
Address的
protocol FormRepresentable {
associatedtype ValueWrapper : Validator
func valueForDetail(valueWrapper: ValueWrapper) -> String
}
的
struct AnyAddress : Address {
private var _base: Address
var addressLine1: String {
get {return _base.addressLine1}
set {_base.addressLine1 = newValue}
}
var country: String {
get {return _base.country}
set {_base.country = newValue}
}
var city: String {
get {return _base.city}
set {_base.city = newValue}
}
init(_ base: Address) {
_base = base
}
}
的
enum AddressFrom : Int, FormRepresentable {
// ...
func valueForDetail(valueWrapper: AnyAddress) -> String {
// ...
}
}
答案 1 :(得分：0)
您有几个问题：
首先，您实际上并未声明Address实现Validator
//Address inherits Validator
protocol Address : Validator {
var addressLine1: String {get set}
var city: String {get set}
var country: String {get set}
}
并且您没有声明ValueWrapper的关联类型：
typealias ValueWrapper = ShippingAddress
你似乎真的想让AddressFrom.valueForDetail取一个ShippingAddress：
func valueForDetail(valueWrapper: ShippingAddress) -> String {
switch self {
case .Address1:
return valueWrapper.addressLine1
case .City:
return valueWrapper.city
case .Country:
return valueWrapper.country
}
}
总而言之，它看起来像：
enum ValidationResult {
case Success
case Failure(String)
}
protocol Validator {
func validate() -> ValidationResult
}
//Address inherits Validator
protocol Address : Validator {
var addressLine1: String {get set}
var city: String {get set}
var country: String {get set}
}
////Fulfill Validator protocol requirements in extension
extension Address {
func validate() -> ValidationResult {
if addressLine1.isEmpty {
return .Failure("Address can not be empty")
}
return .Success
}
}
protocol FormRepresentable {
associatedtype ValueWrapper: Validator
func valueForDetail(valueWrapper: ValueWrapper) -> String
}
// Shipping Address conforming to Address protocol.
// It should also implicity conform to Validator since
// Address inherits from Validator?
struct ShippingAddress: Address {
var addressLine1 = "CA"
var city = "HYD"
var country = "India"
}
// While compiling, it says:
// Inferred type 'Address' (by matching requirement 'valueForDetail') is invalid: does not conform
// to 'Validator'.
// But Address confroms to Validator.
enum AddressFrom: Int, FormRepresentable {
case Address1
case City
case Country
// define associated type for FormRepresentable
typealias ValueWrapper = ShippingAddress
func valueForDetail(valueWrapper: ShippingAddress) -> String {
switch self {
case .Address1:
return valueWrapper.addressLine1
case .City:
return valueWrapper.city
case .Country:
return valueWrapper.country
}
}
}