Is there anyway I can avoid the use of what appears to be some "boilerplate" code? - swift

Question

I am starting with a function that looks like this:
func getUser(command: APICommand, id: Int, handler: (apiResponse: APIResponse<User>) -> Void ) {
let url = apiPath + "users/\(id)"
Alamofire.request(.GET, url, parameters: requestParameters)
.responseObject { (a:NSURLRequest, b:NSHTTPURLResponse?, c:User?, d:AnyObject?, e:NSError? ) in
let apiResponse = APIResponse(command: command,request: a, response: b, swiftObject: c, rawObject: d, error: e)
if AlamofireAPIRequestRepository.resultIsRetryableError(e, command: command) {
println("retrying request")
command.retry()
} else {
handler(apiResponse: apiResponse)
}
}
}
I am going to have a number of functions that look very similar such as, getUserList() for example.
Looking at this I realized the entire Alamofire.request call is going to be pretty much boiler plate code. The only difference will be the Type of argument c passed into the closure that gets called by the responseObject() method. In this case it is User? , in the getUserList() method it will be UserList?
Is there any way I can make this more generic and avoid what appears to be just "boilerplate" code?
I Here is what I have tried.
func alamofireGetRequest<T>(url: URLStringConvertible, parameters: [String: AnyObject]?,
command: APICommand, handler: (apiResponse: APIResponse<T>) -> Void) -> Void {
Alamofire.request(.GET, url, parameters: parameters)
.responseObject { (a:NSURLRequest, b:NSHTTPURLResponse?, c:T?, d:AnyObject?, e:NSError? ) in
let apiResponse = APIResponse(command: command,request: a, response: b, swiftObject: c, rawObject: d, error: e)
if AlamofireAPIRequestRepository.resultIsRetryableError(e, command: command) {
println("retrying request")
command.retry()
} else {
handler(apiResponse: apiResponse)
}
}
}
but the compiler complains with:
Cannot invoke 'responseObject' with an argument list of type
'((NSURLRequest, NSHTTPURLResponse?, T?, AnyObject?, NSError?) -> _)'
and if I replace the c:T? above with c:User? it is happy.
A comment below referred to this question, which may explain why the solution I tried does not work, but does really answer my intended question as to how to avoid this duplicated code.

Answer 1

I think I found an acceptable solution.
Below is the relevant parts of the code, but basically I end up passing in an argument type of AnyObject in to the closure rather than a generic. Before you say that I am cheating you have to understand that my original call would have looked something like this.
func testGetUserRequestSuccess() {
let getUserCommand=commandFactory.createGetUserCommandUsing(apiRepo, id: 1) {
if let swiftObject = $0.swiftObject {
XCTAssertEqual(swiftObject.id!, 1, "id is correct")
}
self.expectation.fulfill()
}
commandProcessor.processCommand(getUserCommand)
wait(5)
}
now it looks like this:
func testGetUserRequestSuccess() {
let getUserCommand=commandFactory.createGetUserCommandUsing(apiRepo, id: 1) {
if let swiftObject = $0.swiftObject as? User {
XCTAssertEqual(swiftObject.id!, 1, "id is correct")
}
self.expectation.fulfill()
}
commandProcessor.processCommand(getUserCommand)
wait(5)
}
so I had to add the as? User cast to the if let statement, which seems reasonable.
relevant code for anyone interested.
The "specialty" code (what will be repeated for each operation)
func getUser(retriesUse retryProcessor: APICommandProcessor, command: APICommand, id: Int, handler: (apiResponse: APIResponse) -> Void ) {
let url = apiPath + "users/\(id)"
Alamofire.request(.GET, url, parameters: requestParameters)
.responseObject { (a:NSURLRequest, b:NSHTTPURLResponse?, c:User?, d:AnyObject?, e:NSError? ) in
let apiResponse = APIResponse(command: command,request: a, response: b, swiftObject: c, rawObject: d, error: e)
self.finishResponse(command, retryProcessor: retryProcessor, apiResponse: apiResponse, handler: handler)
}
}
The common part that I wanted to factor out (mainly a placeholder at this point)
func finishResponse(command: APICommand, retryProcessor: APICommandProcessor, apiResponse: APIResponse, handler: (apiResponse: APIResponse) -> Void) -> Void {
if AlamofireAPIRequestRepository.resultIsRetryableError(apiResponse.error, retryProcessor: retryProcessor, command: command) {
println("retrying \(command)")
retryProcessor.retryCommand(command)
} else {
println("request completed")
handler(apiResponse: apiResponse)
}
}
a supporting struct used above:
struct APIResponse {
let command: APICommand
let request: NSURLRequest
let response: NSHTTPURLResponse?
let swiftObject: AnyObject?
let rawObject: AnyObject?
let error: NSError?
}