Question

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What are the details of “Objective-C Literals” mentioned in the Xcode 4.4 release notes?

I’ve got question about @[] and @{}.

Some code taken from internet:

self.searches = [@[] mutableCopy]; 
self.searchResults = [@{} mutableCopy]; 

1. Is @[] equal to [NSMutableDictionary dictionary]?
2. Is @{} equal to [NSMutableArray array]?

Answer 1

1. No. @[] is equal to [NSArray array] or [[NSArray alloc] init].
2. No. @{} is equal to [NSDictionary dictionary] or [[NSDictionary alloc] init].

(depending on the context and whether you use Automatic Reference Counting (ARC) or not)

That’s why you see things like [@[] mutableCopy] sometimes. This will create an empty immutable array and create a mutable copy of it.

The result is the same as using [NSMutableDictionary dictionary] or [[NSMutableDictionary alloc] init].