An example implementation of Ruby's 'partition' method in Swift.

array_partition.swift

extension Array {
    func partition(iterator: (T) -> Bool) -> (Array<T>, Array<T>) {
        var ifTrue = Array<T>()
        var ifFalse = Array<T>()
        self.each {
            if iterator($0) == true {
                ifTrue.append($0)
            } else {
                ifFalse.append($0)
            }
        }
        return (ifTrue, ifFalse)
    }
}

/*
Example usage: 

var numbersToPart = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
var (even, odd) = numbersToPart.partition { $0 % 2 == 0 }
// even => [2, 4, 6, 8, 10]
// odd  => [1, 3, 5, 7, 9 ]
*/

Depends on this 'each' implentation:

extension Array {
    func each(iterator: (T) -> Void) -> Array {
        for item in self {
            iterator(item)
        }
        return self
    }
}