CODEWITHSUNDEEP
swift
vrwim
vrwim

Reputation: 14340

Weird optional tuple array behavior

I have an array like so:

var array: [(NSDate?, NSData?)] = []

And when I use it like this:

array.append(NSDate(), nil)

The compiler gives the error accessing members of protocol type value 'NSData' is unimplemented

I don't understand this error, it should work right?

Upvotes: 0

Views: 150

Answers (2)

Ian
Ian

Reputation: 12768

It is having difficulty determining the type of the tuple provided in swift when passing nil as a parameter so you must cast it to be the correct type.

var array: [(NSDate?, NSData?)] = []
array.append((NSDate(), nil) as (NSDate?, NSData?))

or 

let t : (NSDate?, NSData?) = (NSDate(), nil)
array.append(t)

Upvotes: 4

rintaro
rintaro

Reputation: 51911

Swift doesn't support conversion like this:

let a:(String, Int?) = ("test", 1)
let b:(String?, Int?) = a
//                      ^ error: cannot express tuple conversion '(String, Int?)' to '(String?, Int?)'

The tuple type must be exactly matched to the destination type.

But, In your case, it can be considered as a bug. because this works:

func foo(x:(NSDate?, NSData?)) { println(x) }
foo((NSDate(), nil))

But this doesn't:

struct Foo<T> {
    func foo(x:T) { println(x) }
}

var f = Foo<(NSDate?, NSData?)>()
f.foo((NSDate(), nil))

The workaround would be:

array.append((NSDate(), nil) as (NSDate?, NSData?))
// OR
array.append((NSDate() as NSDate?, nil as NSData?))
// OR
array.append(NSDate() as NSDate?, nil as NSData?)

Upvotes: 1

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