Swift可选参数功能

Question

So I have the following function:

func remoteCall(_url:String, _params:[String: String]?=nil){
   ...


   ...
   Alamofire.request(.POST, _url, parameters: _params)   //requires _params to be of type [String String!]

   ...
}

As you can see, I can do:

let url = "https://eamorr.com/remote.php"
remoteCall(url)    //works great!

Or, I can do:

let url = "https://eamorr.com/remote.php"
let params = [
    "email": "eamorr@eamorr.com",
    "pword": "secret"
]
remoteCall(url, _params:params)   //works great!

However, what I can't do is:

let url = "https://eamorr.com/remote.php"
let params = [
    "email": email.text,   //where "email" is a UITextField
    "pword": pword.text    //where "pword" is a UITextField
]
remoteCall(url, _params:params)   //this doesn't work

I get this error:

'String!' is not identical to 'String'

I need to be able to accomodate all three situations (pass nothing, pass raw strings, and pass UITextField values)

Unfortunately, if I try to change the function signature (note the '!' after the keyword "String") to:

func remoteCall(_url:String, _params:[String: String!]?=nil){
   ...

   ...
}

The UITextField values work, passing nil works, but the raw strings situation fails at run-time.

fatal error: can't unsafeBitCast between types of different sizes

EXC_BAD_INSTRUCTION

I'll be using this function a lot, so I would like not to have to wrap my "params" variable up in messy code.

I'm new to Swift, an Objective-C head, and trying to re-learn everything again...

I guess if I can somehow convert any incorrect [String: String] to [String: String!] neatly inside the function without disturbing any nil 's or [String: String!] 's that already work?

Answer 1

I think this should work:

let url = "https://eamorr.com/remote.php"
let params: [String: String] = [ // Note explicitly declared type
    "email": email.text,   //where "email" is a UITextField
    "pword": pword.text    //where "pword" is a UITextField
]
remoteCall(url, _params:params)

Problem in your case was that without explicit type declaration Swift will infer one for you. Both values in the dictionary you create are of String! type, which is different from String . Hence the error. If you explicitly tell Swift that params is of [String: String] type that should work fine because it is ok to assign String! value to a String variable.