Combine two dates specify which components you want to retain from each one

Combine2DatesWithSpecifiedComponents.swift

extension Date {
    
    /// Note: Any duplicate found from 2 components will return nil
    func combine(_ date1Comp: Set<Calendar.Component>, with date2: Date, components date2Comp: Set<Calendar.Component>) -> Date? {
        
        // Check if has duplicates
        let date1CompDict: [Calendar.Component: Bool] = {
            var dict: [Calendar.Component: Bool] = [:]
            date1Comp.forEach{ dict[$0] = true }
            return dict
        }()
        for component in date2Comp {
            if date1CompDict[component] != nil {
                print("found duplicate")
                return nil
            }
        }
        
        let cal = Calendar.current
        let d1C = cal.dateComponents(date1Comp, from: self)
        let d2C = cal.dateComponents(date2Comp, from: date2)
        
        var mergedComponents = DateComponents()
        mergedComponents.year = d1C.year != nil ? d1C.year: d2C.year
        mergedComponents.month = d1C.month != nil ? d1C.month: d2C.month
        mergedComponents.day = d1C.day != nil ? d1C.day: d2C.day
        mergedComponents.hour = d1C.hour != nil ? d1C.hour: d2C.hour
        mergedComponents.minute = d1C.minute != nil ? d1C.minute: d2C.minute
        mergedComponents.second = d1C.second != nil ? d1C.second: d2C.second
        
        return cal.date(from: mergedComponents)
    }
}