CODEWITHSUNDEEP
objective-cnsdictionary
吴志坚
吴志坚

Reputation: 29

is NSDictionary non-ordered completely

As we know,NSDictionary is non-ordered.however,when keys is number,when the dictionary is printed,they are printed by ascending number. i have try many times.

Upvotes: 1

Views: 71

Answers (1)

vikingosegundo
vikingosegundo

Reputation: 52237

the order of a dictionary depends on the value that is returned by the hash method of the added key-object. it is very like, that NSNumber returns its value, it is was created with an Integer. in that case your observation would be correct.

more infos: http://bynomial.com/blog/?p=73

try ing this code

NSArray *numbers = @[@0,@1,@2,@3];
for (NSNumber *n in numbers) {
    NSLog(@"%ld:%@", (unsigned long)[n hash], n);
}

it produces this output

0:0
2654435761:1
5308871522:2
7963307283:3

seems as if Knuth's hash algorithm was implemented half.

The original is

hash(i)=i*2654435761 mod 2^32

here it seems to be just

hash(i)=i*2654435761

Upvotes: 1

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