# NSData vs Data write to string differently? **URL:** \ **Category:** Using Swift\ **Created:** [September 22, 2016, 10:31pm UTC](https://forums.swift.org/t/nsdata-vs-data-write-to-string-differently/4087 "2016-09-22T22:31:36Z")\ **Posts on this page:** 4\ **Page:** 1
**Author:** ![robnik](https://avatars.discourse-cdn.com/v4/letter/r/46a35a/32.png) [@robnik](https://forums.swift.org/u/robnik)\ **Post date:** [September 22, 2016, 10:31pm UTC](https://forums.swift.org/t/nsdata-vs-data-write-to-string-differently/4087/1 "2016-09-22T22:31:36Z")
Hi, I’ve run into a problem when updating to new Swift in Xcode 8. There was some NSData in a string like this:         “ … \(data) … “ It changed to type `Data`, and the string went from hexadecimal bytes to writing “20 bytes”. I’m doing a quick bug fix app release now. I can’t remember if Xcode auto converted this for me. I thought it did. ? Either way… seems like they should behave the same here, no? Rob ---
**Author:** ![Shawn\_Erickson](https://sea2.discourse-cdn.com/swift/user_avatar/forums.swift.org/shawn_erickson/32/2981_2.png) [@Shawn\_Erickson](https://forums.swift.org/u/Shawn_Erickson)\ **Post date:** [September 22, 2016, 11:04pm UTC](https://forums.swift.org/t/nsdata-vs-data-write-to-string-differently/4087/2 "2016-09-22T23:04:14Z")
In general you shouldn't depend on what description returns for classes, etc. outside of your control unless it is documented (e.g. part of the API contract). If you want a specific output you should code up something to format the output as you need. -Shawn > **···** > > On Thu, Sep 22, 2016 at 3:33 PM Robert Nikander via swift-users \< swift-users@swift.org\> wrote: > > > Hi, > > > > I’ve run into a problem when updating to new Swift in Xcode 8. There was > > some NSData in a string like this: > > > >     “ … \(data) … “ > > > > It changed to type `Data`, and the string went from hexadecimal bytes to > > writing “20 bytes”. I’m doing a quick bug fix app release now. I can’t > > remember if Xcode auto converted this for me. I thought it did. ? Either > > way… seems like they should behave the same here, no? > > > > Rob > > > > \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ > > swift-users mailing list > > swift-users@swift.org > > [https://lists.swift.org/mailman/listinfo/swift-users](https://lists.swift.org/mailman/listinfo/swift-users) ---
**Author:** ![Joe\_Groff](https://sea2.discourse-cdn.com/swift/user_avatar/forums.swift.org/joe_groff/32/1929_2.png) [@Joe\_Groff](https://forums.swift.org/u/Joe_Groff)\ **Post date:** [September 23, 2016, 1:47am UTC](https://forums.swift.org/t/nsdata-vs-data-write-to-string-differently/4087/3 "2016-09-23T01:47:14Z")
> In general you shouldn't depend on what description returns for classes, etc. outside of your control unless it is documented (e.g. part of the API contract). If you want a specific output you should code up something to format the output as you need. This is good advice, but the printing behavior of Data nonetheless strikes me as a bug. NSData's printing behavior seems much more useful than Data's. If either of you have a moment, would you be able to file a bug about this? -Joe > **···** > > > On Sep 22, 2016, at 4:04 PM, Shawn Erickson via swift-users \ wrote: > > > -Shawn > > > > On Thu, Sep 22, 2016 at 3:33 PM Robert Nikander via swift-users \ wrote: > > Hi, > > > > I’ve run into a problem when updating to new Swift in Xcode 8. There was some NSData in a string like this: > > > >     “ … \(data) … “ > > > > It changed to type `Data`, and the string went from hexadecimal bytes to writing “20 bytes”. I’m doing a quick bug fix app release now. I can’t remember if Xcode auto converted this for me. I thought it did. ? Either way… seems like they should behave the same here, no? > > > > Rob > > > > \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ > > swift-users mailing list > > swift-users@swift.org > > [https://lists.swift.org/mailman/listinfo/swift-users](https://lists.swift.org/mailman/listinfo/swift-users) > > \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ > > swift-users mailing list > > swift-users@swift.org > > [https://lists.swift.org/mailman/listinfo/swift-users](https://lists.swift.org/mailman/listinfo/swift-users) ---
**Author:** ![Martin](https://avatars.discourse-cdn.com/v4/letter/m/73ab20/32.png) [@Martin](https://forums.swift.org/u/Martin)\ **Post date:** [September 23, 2016, 3:15am UTC](https://forums.swift.org/t/nsdata-vs-data-write-to-string-differently/4087/4 "2016-09-23T03:15:30Z")
I had filed a related bug   [[SR-2514] Add a "hex dump" method to `Data` · Issue #4115 · apple/swift-corelibs-foundation · GitHub](https://bugs.swift.org/browse/SR-2514)   Add a "hex dump" method to `Data` as a result of the discussion starting at   [[swift-users] No hex dump anymore in Data description](https://lists.swift.org/pipermail/swift-users/Week-of-Mon-20160822/003035.html) Martin > **···** > > > On 23 Sep 2016, at 03:47, Joe Groff via swift-users \ wrote: > > > > > On Sep 22, 2016, at 4:04 PM, Shawn Erickson via swift-users \ wrote: > > > > > > In general you shouldn't depend on what description returns for classes, etc. outside of your control unless it is documented (e.g. part of the API contract). If you want a specific output you should code up something to format the output as you need. > > > > This is good advice, but the printing behavior of Data nonetheless strikes me as a bug. NSData's printing behavior seems much more useful than Data's. If either of you have a moment, would you be able to file a bug about this? > > > > -Joe > > > > > -Shawn > > > > > > On Thu, Sep 22, 2016 at 3:33 PM Robert Nikander via swift-users \ wrote: > > > Hi, > > > > > > I’ve run into a problem when updating to new Swift in Xcode 8. There was some NSData in a string like this: > > > > > >    “ … \(data) … “ > > > > > > It changed to type `Data`, and the string went from hexadecimal bytes to writing “20 bytes”. I’m doing a quick bug fix app release now. I can’t remember if Xcode auto converted this for me. I thought it did. ? Either way… seems like they should behave the same here, no? > > > > > > Rob > > > > > > \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ > > > swift-users mailing list > > > swift-users@swift.org > > > [https://lists.swift.org/mailman/listinfo/swift-users](https://lists.swift.org/mailman/listinfo/swift-users) > > > \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ > > > swift-users mailing list > > > swift-users@swift.org > > > [https://lists.swift.org/mailman/listinfo/swift-users](https://lists.swift.org/mailman/listinfo/swift-users) > > > > \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ > > swift-users mailing list > > swift-users@swift.org > > [https://lists.swift.org/mailman/listinfo/swift-users](https://lists.swift.org/mailman/listinfo/swift-users)