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

import Foundation

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

extension NSCalendar {
    func dateRange(startDate startDate: NSDate, endDate: NSDate, stepUnits: NSCalendarUnit, stepValue: Int) -> DateRange {
        let dateRange = DateRange(calendar: self, startDate: startDate, endDate: endDate, stepUnits: stepUnits, stepValue: stepValue, multiplier: 0)
        return dateRange
    }
}

struct DateRange : SequenceType {
    
    var calendar: NSCalendar
    var startDate: NSDate
    var endDate: NSDate
    var stepUnits: NSCalendarUnit
    var stepValue: Int
    private var multiplier: Int
    
    func generate() -> Generator {
        return Generator(range: self)
    }
    
    struct Generator: GeneratorType {
        
        var range: DateRange
        
        mutating func next() -> NSDate? {
            guard let nextDate = range.calendar.dateByAddingUnit(range.stepUnits,
                                                          value: range.stepValue * range.multiplier,
                                                         toDate: range.startDate,
                                                        options: []) else {
                return nil
            }
            if nextDate > range.endDate {
                return nil
            }
            else {
                range.multiplier += 1
                return nextDate
            }
        }
    }
}

// Usage:
func testDateRange() {
    let calendar = NSCalendar(calendarIdentifier: NSCalendarIdentifierGregorian)!
    let startDate = NSDate(timeIntervalSinceNow: 0)
    let endDate = NSDate(timeIntervalSinceNow: 24*60*60*7-1)
    let dateRange = calendar.dateRange(startDate: startDate,
                                       endDate: endDate,
                                       stepUnits: .Day,
                                       stepValue: 1)
    let datesInRange = Array(dateRange)
    XCTAssertEqual(datesInRange.count, 7, "Expected 7 days")
    XCTAssertEqual(datesInRange.first, startDate, "First date should have been the start date.")
}

The one issue I've found with this, is it seems to skip over the first date you pass to it. I.e. Date 1 (exclusive) to Date N (inclusive)

The one issue I've found with this, is it seems to skip over the first date you pass to it. I.e. Date 1 (exclusive) to Date N (inclusive)

Yes, the start index is non-inclusive. I guess one needs to implement constructor that will subtract 1 day from start index.

Yes, the start index is non-inclusive. I guess one needs to implement constructor that will subtract 1 day from start index.

Thanks for the comments pointing out the issue with the first date! I've updated the gist to fix that issue, as well as changed it to be created using an extension on NSCalendar, which I think is more idiomatic for NSCalendar-related date functions.

Thanks for the comments pointing out the issue with the first date! I've updated the gist to fix that issue, as well as changed it to be created using an extension on NSCalendar, which I think is more idiomatic for NSCalendar-related date functions.

I'm guessing it's not that easy to create an option to iterate backwards through the range?

I'm guessing it's not that easy to create an option to iterate backwards through the range?

I move from swift 2.2 to swift 3.0. Which is getting lot of errors. can you help in converting to swift 3.0

I move from swift 2.2 to swift 3.0. Which is getting lot of errors. can you help in converting to swift 3.0

@Nidhee you probably don't need this still, but I updated for Swift 3 today :)

@Nidhee you probably don't need this still, but I updated for Swift 3 today :)

For Swift 4:

extension Calendar {
    func dateRange(startDate: Date, endDate: Date, component: Calendar.Component, step: Int) -> DateRange {
        let dateRange = DateRange(calendar: self, startDate: startDate, endDate: endDate, component: component, step: step, multiplier: 0)
        return dateRange
    }
}

struct DateRange : Sequence, IteratorProtocol {
    var calendar: Calendar
    var startDate: Date
    var endDate: Date
    var component: Calendar.Component
    var step: Int
    var multiplier: Int
        
    mutating func next() -> Date? {
        guard let nextDate = calendar.date(byAdding: component, value: step * multiplier, to: startDate)
        else {
            return nil
        }
        
        if nextDate > endDate {
            return nil
        } else {
            multiplier += 1
            return nextDate
        }
    }
}

For Swift 4:

extension Calendar {
    func dateRange(startDate: Date, endDate: Date, component: Calendar.Component, step: Int) -> DateRange {
        let dateRange = DateRange(calendar: self, startDate: startDate, endDate: endDate, component: component, step: step, multiplier: 0)
        return dateRange
    }
}

struct DateRange : Sequence, IteratorProtocol {
    var calendar: Calendar
    var startDate: Date
    var endDate: Date
    var component: Calendar.Component
    var step: Int
    var multiplier: Int
        
    mutating func next() -> Date? {
        guard let nextDate = calendar.date(byAdding: component, value: step * multiplier, to: startDate)
        else {
            return nil
        }
        
        if nextDate > endDate {
            return nil
        } else {
            multiplier += 1
            return nextDate
        }
    }
}