如何在Swift中定义初始化泛型类型

Question

I'm writing the function like this

func issueArrayFromResponse(response: DataResponse<Any>) -> Result<[Issue]> {}

However this kind of function appear many time, such as repoArrayFromResponse, gistArrayFromRespnse and so on. So I tried to make these functions into one.

func arrayFromResponse<T>(response: DataResponse<Any>) -> Result<[T]> {}

The problem is I don't have initializer for type T and don't know how to achieve it. In case issueArrayFromResponse , I have a class Issue and it has initializer: init(json: [[String: Any]]), so i was able to write

issue = Issue(json: item)

However, in case arrayFromResponse<T> , the compiler says 'T' cannot be constructed because it has no accessible initializers

How can I make initializer for T?

Answer 1

I think the easiest way is to make protocol. You can make such protocol:

protocol ResultProtocol {   
}

and confirm all your classes to this protocol

class Issue: ResultProtocol {
    init(json: String) {

    }
}

then you can:

func arrayFromResponse<T: ResultProtocol>(response: DataResponse<Any>) -> Result<[T]> {

    return Result<[T]>()

}