Re: Objective-C basics - (Why NSNumber conforms to NSCopying protocol)
Re: Objective-C basics - (Why NSNumber conforms to NSCopying protocol)
- Subject: Re: Objective-C basics - (Why NSNumber conforms to NSCopying protocol)
- From: Quincey Morris <email@hidden>
- Date: Thu, 11 Aug 2016 00:04:42 -0700
- Feedback-id: 167118m:167118agrif8a:167118szerIvDxml:SMTPCORP
On Aug 10, 2016, at 23:32 , Sasikumar JP <email@hidden> wrote:
>
> what was the reason NSNumber conforms to NSCopying protocol.
1. It actually inherits conformance from its superclass, NSValue.
2. The fact than an object is immutable does not (in general) mean that a copy can be represented by the same object reference. For example, an object that contained its own date of creation might be immutable, but a copy might have a different date, and therefore be a different object. Putting this another way, the immutability does not make NSCopying conformance irrelevant.
3. NSNumber is one of a group of classes that represent “serializable” objects (for property lists, for example). Since these are often arranged in heterogenous hierarchies using arrays, sets and dictionaries, it’s convenient that they share behavior. If all property list classes conform to NSCopying, then property lists can be deep copied without special code.
4. Objects used as NSDictionary keys must conform to NSCopying. It would be a hardship if this excluded NSNumber.
So it turns out to be easier to have NSNumber conform to NSCopying, than to avoid conformance.
_______________________________________________
Cocoa-dev mailing list (email@hidden)
Please do not post admin requests or moderator comments to the list.
Contact the moderators at cocoa-dev-admins(at)lists.apple.com
Help/Unsubscribe/Update your Subscription:
This email sent to email@hidden