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extension Date {

    //An integer representation of age from the date object (read-only).
    var age: Int {
        get {
            let now = Date()
            let calendar = Calendar.current

            let ageComponents = calendar.dateComponents([.year], from: self, to: now)
            let age = ageComponents.year!
            return age
        }
    }

    init(year: Int, month: Int, day: Int) {
        var dc = DateComponents()
        dc.year = year
        dc.month = month
        dc.day = day

        var calendar = Calendar(identifier: .gregorian)
        calendar.timeZone = TimeZone(secondsFromGMT: 0)!
        if let date = calendar.date(from: dc) {
            self.init(timeInterval: 0, since: date)
        } else {
            fatalError("Date component values were invalid.")
        }
    }

}

let dob = Date(year: 1975, month: 1, day: 1)
let age = dob.age

print(age)

extension Date {
    var age: Int {
        return Calendar.current.dateComponents([.year], from: self, to: Date()).year!
    }
}

let myDOB = Calendar.current.date(from: DateComponents(year: 1970, month: 9, day: 10))!

let myAge = myDOB.age      // 46