在泛型上尾随闭包？
在泛型上尾随闭包？
提问于 2016-01-09 16:36:22
嗨，我正在试着理解以下来自阿拉莫火的代码。如何用"{}“初始化一个结构--我知道你可以用尾随闭包来调用一个闭包。我知道我完全错过了什么，但是什么？
extension Request {
public func responseObject<T: ResponseObjectSerializable>(completionHandler: Response<T, NSError> -> Void) -> Self {
let responseSerializer = ResponseSerializer<T, NSError> { // What is this?
request, response, data, error in
guard error == nil else { return .Failure(error!) }
let JSONResponseSerializer = Request.JSONResponseSerializer(options: .AllowFragments)
let result = JSONResponseSerializer.serializeResponse(request, response, data, error)
switch result {
case .Success(let value):
if let
response = response,
responseObject = T(response: response, representation: value)
{
return .Success(responseObject)
} else {
let failureReason = "JSON could not be serialized into response object: \(value)"
let error = Error.errorWithCode(.JSONSerializationFailed, failureReason: failureReason)
return .Failure(error)
}
case .Failure(let error):
return .Failure(error)
}
}
return response(responseSerializer: responseSerializer, completionHandler: completionHandler)
}
}阿拉莫火的结构ResponseSerializer
public struct ResponseSerializer<Value, Error: ErrorType>: ResponseSerializerType {
/// The type of serialized object to be created by this `ResponseSerializer`.
public typealias SerializedObject = Value
/// The type of error to be created by this `ResponseSerializer` if serialization fails.
public typealias ErrorObject = Error
/**
A closure used by response handlers that takes a request, response, data and error and returns a result.
*/
public var serializeResponse: (NSURLRequest?, NSHTTPURLResponse?, NSData?, NSError?) -> Result<Value, Error>
/**
Initializes the `ResponseSerializer` instance with the given serialize response closure.
- parameter serializeResponse: The closure used to serialize the response.
- returns: The new generic response serializer instance.
*/
public init(serializeResponse: (NSURLRequest?, NSHTTPURLResponse?, NSData?, NSError?) -> Result<Value, Error>) {
self.serializeResponse = serializeResponse
}
}回答 2
Stack Overflow用户
回答已采纳
发布于 2016-01-09 17:01:24
你的问题可以大大减少(而且应该是这样)。以下是ResponseSerializer的相关声明：
public struct ResponseSerializer<Value, Error: ErrorType>: ResponseSerializerType {
public init(serializeResponse: (NSURLRequest?, NSHTTPURLResponse?, NSData?, NSError?) -> Result<Value, Error>) {
self.serializeResponse = serializeResponse
}
}因此，这个初始化器init(serializeResponse:)接受一个参数--一个函数接受四个参数，并返回一个参数(指定类型的参数)。
因此，我们可以像这样初始化：
func f (request:NSURLRequest?, response:NSHTTPURLResponse?, data:NSData?, error:NSError?) -> Result<Value, Error>) {
guard error == nil else { return .Failure(error!)
}
let responseSerializer = ResponseSerializer<T, NSError>(serializeResponse:f)然而，这是可以浓缩的。我们实际上不需要函数f，所以我们可以将其作为匿名函数提供；它不需要名称或完整的声明。此外，对于匿名函数有一个“快捷”规则，如果匿名函数是函数的最后一个参数，则可以在函数的结束括号之后按字面顺序提供它，并省略参数名称。如果该函数不接受其他参数，则可以完全省略它的括号。
嗯，这个init正是这样一个函数--它接受一个函数作为它的最后(也是唯一)参数--所以这正是所讨论的代码所做的：
let responseSerializer = ResponseSerializer<T, NSError> {
request, response, data, error in
guard error == nil else { return .Failure(error!)
}Stack Overflow用户
发布于 2016-01-09 17:01:44
如果我正确地阅读了这些代码，那么上面的代码有一个类似的模式：
// just a something
struct Blah {
var stuffs : (message:String) -> Void
init(closure:(message:String) -> Void) {
self.stuffs = closure
}
}
// an extension because the code above is also in an extension, but not needed at all
extension Blah {
// a function with a closure that also returns an instance of Self
func spawnChild(closure:(message:String) -> Void) -> Blah {
return Blah(closure: closure) // closure is passed to spawn
}
}测试：
let alpha = Blah { (message) -> Void in
print("alpha",message)
}
let beta = alpha.spawnChild { (message) -> Void in
print("beta", message)
}
alpha.stuffs(message: "parrent") // alpha parent
beta.stuffs(message: "spawn") // beta spawn请记住，尾随闭包只是输入参数(即闭包)的语法糖。因此，任何接受输入参数的都会有一个尾随闭包。
页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/34696042
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