Custom Sequence

gistfile1.swift

class Times2Generator : Generator {
    typealias Element = (original: Int,timestwo: Int)?
    func next() -> Element? {
        if  source.count > 0 {
            let result = self.source[0]
            source = Array(source[1..source.count])
            return (result,result * 2)
        }
        else {
            return .None
        }
    }
    
    init(s: Int[]) { self.source = s }
    
    var source : Array<Int>!
}


class Times2Sequence : Sequence {
    var values : Array<Int>
    
    init(v : Array<Int>) {self.values = v}
    
    // typealias can be inferred so could be left out
    typealias GeneratorType = Times2Generator
    func generate() -> Times2Generator {
        return Times2Generator(s: values)
    }
    
}


let ms = Times2Sequence(v: [1,2,5,10,20])

typealias T = Times2Sequence.GeneratorType.Element

for timesTwo : T in ms {
    let (x,y) = timesTwo!
    println("\(x) * 2 is \(y)")
}