Re: Best Practice for Returning Immutable Objects?

[Karl Moskowski]

On 3-Jun-08, at 12:23 PM, [EMAIL PROTECTED] wrote:

Karl Moskowski wrote on 2008-06-03 17:16:48:

On 3-Jun-08, at 12:13 PM, Mike Abdullah wrote:

Well this cast is fairly pointless as it makes no change to the data
at all. Returning an NSMutableData object from an NSData method is
perfectly legitimate as it is a subclass. So you might as well just
do:

  return myData;

Really, it's up to you. You can just use the simple option of
returning a mutable object, or you can do either of these:

  return [NSData dataWithData:myData];

  return [[myData copy] autorelease];

My concern is that the returned object be truly immutable. For now,
I'm the only one using the class, but that may change in the future.

If it has to be 'truly' immutable, then use one of Mike's suggestions,

which is what tells the ObjC runtime what class the instance is.  I.e.
given an NSMutableData *foo:
(NSData *)foo "is a" NSMutableData
(NSObject *)foo "is a" NSMutableData
(id) foo "is a" NSMutableData

which will return an immutable NSData object containing the same bytes as the bytes in the mutable object you constructed. The code you originally posted still returns the mutable object; casting doesn't change the 'isa'

Maybe "truly" was too strong a word. :-)



Thanks.

----
Karl Moskowski <[EMAIL PROTECTED]>
Voodoo Ergonomics Inc. <http://voodooergonomics.com/>

Since I can expect people to follow the conventions defined by the API, I'll just cast and expect the callers not to mutate.

smime.p7s
Description: S/MIME cryptographic signature

_______________________________________________

Cocoa-dev mailing list (Cocoa-dev@lists.apple.com)

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:
http://lists.apple.com/mailman/options/cocoa-dev/archive%40mail-archive.com

This email sent to [EMAIL PROTECTED]