我正在嘗試進行一些依賴注入以進行單元測驗，并使 iOS 實時預覽更容易。
我有一個Store協議，我想在我的 SUT 類中使用它們，這樣我就可以傳遞模擬實作。
protocol Store {
associatedtype AnyData
func load() -> AnyData?
func save(data anyData: AnyData)
}
class FileStore<AnyData: Codable>: Store {
func load() -> AnyData? { /* Actual code that saves to a file */ }
func save(data anyData: AnyData) { /* Actual code that saves to a file */ }
}
class MockStore<AnyData: Codable>: Store {
func load() -> AnyData? { /* Returns mocked value for unit testing */ }
func save(data anyData: AnyData) { /* Returns mocked value for unit testing */ }
}
但是，在我的 SUT 課程中，我有以下內容：
class MyClassToBeTested {
// THIS DOESN'T WORK
let bookStore: Store // ERROR: Protocol 'Store' can only be used as a generic
// constraint because it has Self or associated type requirements
// DOESN'T WORK EITHER
let studentStore: Store<Student> // ERROR: Cannot specialize non-generic type 'Store'
}
// in real app
MyClassToBeTested(
bookStore: FileStore<Book>()
studentStore: FileStore<Student>()
)
// in test or preview
MyClassToBeTested(
bookStore: MockStore<Book>()
studentStore: MockStore<Student>()
)
好像我被卡住了。我本質上是在嘗試擁有一個通用協議，類似于 Java 中的通用介面。我錯過了什么？
更新
在@Jessy 回答之后，我做到了：
class MyClassToBeTested<BookStore: Store, StudentStore: Store>
where
BookStore.AnyData == Book,
StudentStore.AnyData == Student
{
let bookStore: BookStore
let studentStore: StudentStore
這解決了一半的問題。另一半是如何使用它鍵入變數：
class OtherClass {
var sut: MyClassToBeTested // ERROR: Generic parameter Bookstore could not be inferred
var sut2: MyClassToBeTested< // I know this isn't supported in Swift
Store<Book>, // but can't figure out the right syntax
Store<Student> // ERROR: Cannot specialize non-generic type 'Store'
> // ERROR: Protocol 'Store' as a type cannot conform to the protocol itself
var sut3: MyClassToBeTested< // Compiles, BUT I cannot pass a
FileStore<Book>, // MockStore in my tests/preview
FileStore<Student> // so it's useless
>
}
uj5u.com熱心網友回復：
該
Store<Student>語法從未得到支持，但最近 Swift 論壇上有很多關于它的討論——可能很快就會支持。Stack Overflow 上還有許多其他關于無法使用具有關聯型別（如存在）的協議的 Q/A——它終于可用，但僅在 Xcode 13.3（測驗版）中可用。
在我看來，您希望事情受到這樣的限制：
class MyClassToBeTested<BookStore: Store, StudentStore: Store>
where
BookStore.AnyData == Book,
StudentStore.AnyData == Student
{
let bookStore: BookStore
let studentStore: StudentStore
如果沒有，從 Xcode 13.3 開始可用的最新語法是
class MyClassToBeTested<StudentStore: Store>
where StudentStore.AnyData == Student {
let bookStore: any Store
let studentStore: StudentStore
init(
bookStore: any Store,
studentStore: StudentStore
) {
self.bookStore = bookStore
self.studentStore = studentStore
}
}
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