Experimenting with creating a SequenceType for iterating over a range of dates. Blogged here: http://adampreble.net/blog/2014/09/iterating-over-range-of-dates-swift/

DateRange.swift

func < (left: NSDate, right: NSDate) -> Bool {
    return left.compare(right) == NSComparisonResult.OrderedAscending
}

struct DateRange : SequenceType {
    
    var calendar: NSCalendar
    var startDate: NSDate
    var endDate: NSDate
    var stepUnits: NSCalendarUnit
    var stepValue: Int
    
    func generate() -> Generator {
        return Generator(range: self)
    }
    
    struct Generator: GeneratorType {
        
        var range: DateRange
        
        mutating func next() -> NSDate? {
            let nextDate = range.calendar.dateByAddingUnit(range.stepUnits,
                                                    value: range.stepValue,
                                                   toDate: range.startDate,
                                                  options: NSCalendarOptions.allZeros)
            if range.endDate < nextDate {
                return nil
            }
            else {
                range.startDate = nextDate
                return nextDate
            }
        }
    }
}

// Usage:
func testDateRange() {
    let calendar = NSCalendar(calendarIdentifier: NSCalendarIdentifierGregorian)
    let startDate = NSDate(timeIntervalSinceNow: 0)
    let endDate = NSDate(timeIntervalSinceNow: 24*60*60*7)
    let dateRange = DateRange(calendar: calendar, 
                             startDate: startDate,
                               endDate: endDate,
                             stepUnits: NSCalendarUnit.CalendarUnitDay,
                             stepValue: 1)
    var days = 0
    for date in dateRange {
        days++
    }
    XCTAssertEqual(days, 7, "Expected 7 days")
}