Sieve of Eratosthenes in Swift

Sieve.swift

//
//  Sieve.swift
//
// The MIT License (MIT)
//
// Copyright (c) 2016 Erik J. Azar
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in all
// copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
// SOFTWARE.

public func sieveDriver() {
    
    let result = sieve()
    
    let primes = result.enumerate().filter({ $0.0 > 1 && $0.1 == true})
    let composites = result.enumerate().filter({ $0.0 > 1 && $0.1 == false})
    
    print("Total Primes: \(primes.count)")
    print("Total Componsites: \(composites.count)")
    print("Primes: \(primes)")
    print("Composites: \(composites)")
}

public func sieve() -> [Bool] {
    let start = NSDate.timeIntervalSinceReferenceDate()
    var scratch = [Bool]( count: 4000002, repeatedValue: true)
    for var i=2; i<scratch.count; i++ {
        if ( scratch[i] ) {
            for var k=i+i; k<scratch.count; k+=i {
                scratch[k] = false;
            }
        }
    }
    print(NSDate.timeIntervalSinceReferenceDate() - start)
    return scratch
}