datetime - Swift - Calculating elapsed time takes too long? -

my server call gives me json data date time per piece of data , want calculate time elapsed between , , load data structure. way i'm doing takes way long, there different design practice should using? follow function using right now

func datediff(_ datestr:string) -> string {     var timeago = "10m"      let formatter = dateformatter()     formatter.dateformat = "yyyy-mm-dd' 'hh:mm:ss"     formatter.timezone = nstimezone(name: "ast") as! timezone       let dateformatter = dateformatter()     dateformatter.dateformat = "yyyy-mm-dd' 'hh:mm:ss"     dateformatter.timezone = nstimezone(name: "ast") as! timezone      let = formatter.string(from: date())      if let date = formatter.date(from: datestr){         if let nowdate = formatter.date(from: now){         let components = calendar.current.datecomponents([.day,.hour,.minute,.second], from: date, to: nowdate)         let sec = components.second         let min = components.minute         let hours = components.hour         let days = components.day         if (sec! > 0){             if let secc = sec {                 timeago = "\(secc)s"             }         }         if (min! > 0){             if let minn = min {                 timeago = "\(minn)m"             }            }         if(hours! > 0){             if let hourss = hours {                 timeago = "\(hourss)h"             }         }         if(days! > 0){             if let dayss = days {                 timeago = "\(dayss)d"             }         }     }   }     return timeago } 

for performance reasons, should pull instantiation of date formatter out of method, because that's notoriously computationally intensive.

i'd suggest using datecomponentsformatter simplify formatting of elapsed time.

so, define 2 formatters:

let dateformatter: dateformatter = {     let _formatter = dateformatter()     _formatter.dateformat = "yyyy-mm-dd' 'hh:mm:ss"     _formatter.locale = locale(identifier: "en_us_posix")     _formatter.timezone = timezone(abbreviation: "ast")  // curious; use `timezone(secondsfromgmt: 0)` (i.e. gmt/utc/zulu)     return _formatter }()  let componentsformatter: datecomponentsformatter = {     let _formatter = datecomponentsformatter()     _formatter.maximumunitcount = 1     _formatter.unitsstyle = .abbreviated     return _formatter }() 

and function considerably simplified:

func datediff(_ string: string) -> string? {     guard let date = dateformatter.date(from: string) else { return nil }      return componentsformatter.string(from: date, to: date()) } 

also note that:

• i used timezone directly, rather round-tripping through nstimezone;
• i set locale en_us_posix, should always use if source of date strings web service or database;
• i eliminated conversion of “now” string , back; use date() directly;

the other thing looks suspicious use of ast timezone. date strings saved in gmt/utc/zulu (e.g., rfc 3339 or iso 8601). if have control on that, that's best practice, avoiding problems if users change time zones;