What is the difference between initializing array with
NSArray * array = [NSArray array];
and
NSArray * array = @[];
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2 Answers
@[] is shorthand for:
id a = nil;
NSArray* array = [NSArray arrayWithObjects:&a count:0];
Which is really just shorthand for [NSArray array], for all intents and purposes.
This is a feature added in a particular version of the compiler (and doesn't actually require runtime support for this particular syntax).
It is not at all like the @"" shorthand in that @"" produces a compile time constant and will cause no messaging at runtime. In fact, @"" (any @"sequence") is a special case in that it emits a compile time constant that is realized in the runtime with zero messaging; zero dynamism. A @"..." is more similar to an Objective-C class than it is to a regular instance of an object.
2 Comments
Basem Saadawy
I think @"" produces an NSString object not a compile time constant.
bbum
Nope; it really is a compile time constant that is loaded via the dynamic linker just like classes and other compile time emitted data. There is no messaging involved.
NSArray * array = @[]; is the new way of doing NSArray * array = [NSArray array];
3 Comments
bbum
A good guess, but mostly incorrect. First statement is correct, rest is wrong.
Mikael
yes, that is correct. Wrote my answer to quickly. Edited my answer. My bad.