CODEWITHSUNDEEP
objective-c
ryanrhee
ryanrhee

Reputation: 2571

NSDictionary - (for id foo in dict) vs (for NSString *foo in [dict allKeys])

Suppose there is an NSDictionary *dict. What is the difference between the following?

for (id key in dict) {
  NSLog(@"value: %@", dict[key]);
}

for (id key in [dict allKeys]) {
  NSLog(@"value: %@", dict[key]);
}

I didn't know that the first version existed, and when I saw it I thought it would be a compile-time error.

Upvotes: 1

Views: 74

Answers (3)

Gerd K
Gerd K

Reputation: 2993

The first variant uses NSDictionaries implementation of "fast enumeration" (NSFastEnumeration Protocol), while the second uses the NSArray implementation. I suspect that the first variant would be ever so slightly faster (at least it is a little less typing).

BTW you can also write

for (NSString *key in dict)
{
     NSLog(@"value: %@", dict[key]);
}

Note that unlike what a previous poster suggests, this is NOT a guarantee that all keys are NSString objects. It merely is an implicit casting of key to NSString *.

Upvotes: 3

Sviatoslav Yakymiv
Sviatoslav Yakymiv

Reputation: 7935

There are no difference. Both versions do the same.

Upvotes: 0

Fortinoh
Fortinoh

Reputation: 104

for (id key in dict) {
  NSLog(@"value: %@", dict[key]);
}

here you are not sure wether your key is NSString or NSNumber or any NSObject

for (NSString *key in [dict allKeys]) {
  NSLog(@"value: %@", dict[key]);
}

whereas in this code snippet you are sure that the keys for the dictionary is NSString

Upvotes: 0

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