On Jan 19, 2010, at 8:53 AM, Shawn Rutledge wrote:
I wish NSDictionary (NSMutableDictionary actually) could handle
arbitrary mappings of one type of object to another, without copying
the keys.
It can. If you have a custom class you want to be able to use as a
dictionary key without copying, then make it implement the NSCopying
protocol and add this method:
- (id) copyWithZone: (NSZone*)zone {
return [self retain];
}
This enables -copy but turns it into a no-op that returns the original
object. (This is perfectly kosher. Most immutable Foundation objects
do the same thing, i.e. copying an immutable NSString returns the same
object.)
Of course you also have to implement -hash and -isEqual: to make your
class play nicely with dictionaries. Make sure these have immutable
semantics: if the values returned by these can ever change, you'll
screw up any dictionary or set the object is in.
I didn't try CFDictionary yet; is that appropriate for an iPhone app?
Yes, you can use CF. Remember that a CFXXXRef is the same as an
NSXXX*, you can just typecast between them. If you create a
CFDictionary you'll have to define your own callbacks, and make the
copy callback just retain the object.
But try NSMapTable first. It's sort of halfway between the two — it's
an Objective-C class but it has greater flexibility in what it can
store and how it stores it.
—Jens_______________________________________________
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