Any way to iterate a tuple in swift?

Question

I am curious how to do a for loop with a tuple in swift.

I know that to access each member you can use dot notation using the index number

var tupleList = ("A",2.9,3,8,5,6,7,8,9)

for each in tupleList {
    println(each)
}

//Error: Type does not conform to protocol sequence

Answer 1

Yes, you can!

func iterate<C,R>(t:C, block:(String,Any)->R) {
    let mirror = reflect(t)
    for i in 0..<mirror.count {
        block(mirror[i].0, mirror[i].1.value)
    }
}

And voila!

let tuple = ((false, true), 42, 42.195, "42.195km")
iterate(tuple) { println("\($0) => \($1)") }
iterate(tuple.0){ println("\($0) => \($1)")}
iterate(tuple.0.0) { println("\($0) => \($1)")} // no-op

Note the last one is not a tuple so nothing happens (though it is a 1-tuple or "Single" which content can be accessed .0, reflect(it).count is 0).

What's interesting is that iterate() can iterate even other types of collection.

iterate([0,1])              { println("\($0) => \($1)") }
iterate(["zero":0,"one":1]) { println("\($0) => \($1)") }

And that collection includes class and struct!

struct Point { var x = 0.0, y = 0.0 }
class  Rect  { var tl = Point(), br = Point() }
iterate(Point()) { println("\($0) => \($1)") }
iterate(Rect())  { println("\($0) => \($1)") }

Caveat: the value passed as the 2nd argument of the block is type Any. You have to cast it back to the values with original type.

Answer 2

You can using reflection Swift 5

Try this in a Playground:

let tuple = (1, 2, "3")
let tupleMirror = Mirror(reflecting: tuple)
let tupleElements = tupleMirror.children.map({ $0.value })
tupleElements

Output:

Answer 3

Swift does not currently support iterating over tuples.

The biggest reasons are:

1. There is no way at runtime to determine the number of elements in a tuple
2. There is no way to access an element at a specific index except for the compile time accessors like tupleList.0. You would really want a subscript tupleList[0] but that is not provided to us

Frankly, I can't see a reason that you would use a tuple instead of an Array if you want to iterate over it.

It doesn't make sense to iterate over a tuple because:

1. Tuples always have a fixed length and each element has a fixed type
2. You can name each tuple member with a name you can use to access it later

Arrays are well made to iterate over:

1. Arbitrary length
2. Can store multiple types using a common superclass or AnyObject
3. Can be declared as a literal in a similar fashion to tuples: var list = ["A",2.9,3,8,5,6,7,8,9]