CODEWITHSUNDEEP
iosswift
user4788711
user4788711

Reputation:

Cast Entry in For in Loop over SequenceType?

Having the following for in loop:

for entry in entries {
   println("entry: \(entry)")
}

I want to cast the entry in the loop header to String. I cannot do the following because it is no Array: 

for entry in entries as! [String] {
}

because entries is not an array.

Edit: entries conforms the SequenceTypeprotocol.

How can I cast entry in the loop header to String?

Upvotes: 1

Views: 129

Answers (2)

Martin R
Martin R

Reputation: 539915

The "easy" solution would be

for x in entries {
    if let y = x as? String {
        println(y)
    }
}

but that is probably not what you are looking for.

If it is acceptable that an array of all elements is created first then the following would work as well:

let a = Array(entries)
for x in a as! [String] {
    println(x)
}

If entries is a sequence producing AnyObject elements, and you know that all these elements are in fact strings, then you can create a new sequence producing Strings with

let stringSeq = SequenceOf { () -> GeneratorOf<String> in
    var gen = entries.generate()
    return GeneratorOf {
        return gen.next() as? String
    }
}

for x in stringSeq {
    println(x) // x is a `String`
}

What you probably should do is to change the definition of the entries generator itself so that it produces strings in the first place. Example (based on the code in your previous question Make Class iterable with a for in Loop? and this blog post):

// Class containing an array of `AnyObject`:
class MyArrayClass {
    var array: [AnyObject] = ["a", "b", "c"]
}

// Sequence producing `String`:
extension MyArrayClass : SequenceType {
    func generate() -> GeneratorOf<String> {
        var index = 0
        return GeneratorOf {
            if index < self.array.count {
                return self.array[index++] as? String
            } else {
                return nil
            }
        }
    }
}

// Now the enumeration gives strings:
let entries = MyArrayClass()
for x in entries {
    println(x)
}

Upvotes: 1

Matteo Piombo
Matteo Piombo

Reputation: 6726

There's map for that ;-)

let entries = NSSet(array: ["Foo", "Bar"])

for entry in map(entries, {$0 as! String}) {
    println("entry: \(entry)")
}

Hope it helps

Upvotes: 2

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