Swift 通用参数'；S'；无法推断

因此，我尝试使用泛型和协议一致性来创建一个小型依赖项注入容器。但是我在编译它时遇到了一些麻烦

我想知道是否有一位敏捷的专家能告诉我问题出在哪里

import Foundation

protocol Service: NSObjectProtocol {
    init()
}

protocol ServicesType {
    func add<S: Service>(service: S.Type)
    func get<S: Service>() throws -> S
}

class Services: ServicesType {

    var services: [Service.Type] = []

    func add<S: Service>(service: S.Type) {
        if services.contains(where: { service -> Bool in return service == service }) { return }
        services.append(service)
    }

    func get<S: Service>() throws -> S {
        guard let first = services.first(where: { service -> Bool in return service == service }) else { throw ServicesTypeError.notFound }
        return first.init() as! S
    }
}

enum ServicesTypeError: Error {
    case notFound
}

---

在操场上做了一点修改后，这个功能就可以正常工作了，但它似乎可以正常工作

如果我是对的（黑体字）

需要：

let creditCardService: **CreditCardService** = try self.services.get()

完整代码：

import Foundation

protocol Service: NSObjectProtocol {
    init()
}

protocol ServicesType {
    func add<S: Service>(service: S.Type)
    func get<S: Service>() throws -> S
}

class Services: ServicesType {

    var services: [Service.Type] = []

    func add<S: Service>(service: S.Type) {
        if services.contains(where: { service -> Bool in return service == service }) { return }
        services.append(service)
    }

    func get<S: Service>() throws -> S {
        guard let first = services.first(where: { service -> Bool in return service == service }) else { throw ServicesTypeError.notFound }
        return first.init() as! S
    }
}

enum ServicesTypeError: Error {
    case notFound
}

class CreditCard {

}

protocol CreditCardServiceType : Service {
    var cards: [CreditCard] { get }
}

class CreditCardService: NSObject, CreditCardServiceType {

    required override init() {
        super.init()
    }
    var cards: [CreditCard] = []
}

let services = Services()
services.add(service: CreditCardService.self)

let creditCardService: CreditCardService = try services.get()

<代码>导入基础 协议服务：NSObjectProtocol{ init（） } 协议服务类型{ func添加（服务：S.Type） func get（）抛出->S } 类别服务：ServicesType{ var服务：[服务.类型]=[] func添加（服务：S.Type）{ if services.contains（其中：{service->Bool in return service==service}）{return} services.append（服务） } func get（）抛出->S{ guard let first=services.first（其中：{service->Bool in return service==service}）else{throw ServicesTypeError.notFound} 首先将.init（）返回为！S } } enum ServicesTypeError:错误{ 未发现病例 } 班级信用卡{ } 协议CreditCardServiceType:服务{ var卡：[信用卡]{get} } CreditCardService类：NSObject，CreditCardServiceType{ 必需的重写初始化（）{ super.init（） } 信用卡：[信用卡]=[] } 让服务=服务（） services.add（服务：CreditCardService.self） 让creditCardService:creditCardService=try services.get（）

---

好的，我的结论如下。虽然没有我想要的那么安全，但已经足够好了

import Foundation

protocol Service: NSObjectProtocol {
    init()
}

protocol ServicesType {

    func add<S: Service>(service: S.Type) throws
    func get<S>() throws -> S

}

class Services: ServicesType {

    var services: [Service.Type] = []

    func add<S: Service>(service: S.Type) throws {
        if services.contains(where: { existing -> Bool in return existing == service }) { throw ServicesTypeError.allReadyAdded}
        services.append(service)
    }

    func get<S>() throws -> S {
        guard let first = services.first(where: { existing -> Bool in return existing is S }) else { throw ServicesTypeError.notFound }
        return first.init() as! S
    }

}

enum ServicesTypeError: Error {
    case allReadyAdded
    case notFound
}

---

如果我将第一段代码粘贴到Playerd中，它在ServicesType上也会失败。还有更多吗？添加了代码的其余部分。我认为@tommysadiqhinrichsens仍然没有提供足够的代码。但出于测试原因，我想隐藏实现类，以便使用具有相同协议的另一个类。这是另一个问题@TommySadiqHinrichsen。让我想一想…@TommySadiqHinrichsen当你添加一个服务时，只需添加它而不需要类型。它应该只是一个实现。当你得到一个服务时，你只需要寻找一个实现该协议的服务。@TommySadiqHinrichsen你会很高兴将其标记为已回答（我得到它是通过推理编译的）。对于你想要的行为，提出一个不同的问题可能是值得的。谢谢这是一个有趣的问题。当然，我只需要让两天过去。

import Foundation

protocol Service: NSObjectProtocol {
    init()
}

protocol ServicesType {
    func add<S: Service>(service: S.Type)
    func get<S: Service>() throws -> S
}

class Services: ServicesType {

    var services: [Service.Type] = []

    func add<S: Service>(service: S.Type) {
        if services.contains(where: { service -> Bool in return service == service }) { return }
        services.append(service)
    }

    func get<S: Service>() throws -> S {
        guard let first = services.first(where: { service -> Bool in return service == service }) else { throw ServicesTypeError.notFound }
        return first.init() as! S
    }
}

enum ServicesTypeError: Error {
    case notFound
}

class CreditCard {

}

protocol CreditCardServiceType : Service {
    var cards: [CreditCard] { get }
}

class CreditCardService: NSObject, CreditCardServiceType {

    required override init() {
        super.init()
    }
    var cards: [CreditCard] = []
}

let services = Services()
services.add(service: CreditCardService.self)

let creditCardService: CreditCardService = try services.get()

import Foundation

protocol Service: NSObjectProtocol {
    init()
}

protocol ServicesType {

    func add<S: Service>(service: S.Type) throws
    func get<S>() throws -> S

}

class Services: ServicesType {

    var services: [Service.Type] = []

    func add<S: Service>(service: S.Type) throws {
        if services.contains(where: { existing -> Bool in return existing == service }) { throw ServicesTypeError.allReadyAdded}
        services.append(service)
    }

    func get<S>() throws -> S {
        guard let first = services.first(where: { existing -> Bool in return existing is S }) else { throw ServicesTypeError.notFound }
        return first.init() as! S
    }

}

enum ServicesTypeError: Error {
    case allReadyAdded
    case notFound
}

try self.services.add(service: ProfileService.self)
let profileService: ProfileServiceType = try self.services.get()