Is there a literal syntax for mutable collections?

问题:

I know I can create an NSArray with @[@"foo", @"bar"] or an NSDictionary with @{@0 : @"foo", @1 : @"bar"}.

Is there a literal syntax for creating an NSMutableArray or an NSMutableDictionary?

回答1:

No. Just as how there isn't a syntax for creating an NSMutableString either. Mutable objects are not particularly suited to literal values.

回答2:

There isn't a built in way, but I just usually use mutableCopy like this:

 NSMutableArray *array = [@[ @"1", @"2", @"3" ] mutableCopy];

回答3:

But, is there a literal syntax for creating an NSMutableArray or an NSMutableDictionary?

No. Best alternative:

[@[ @"foo", @"bar"] mutableCopy]

回答4:

Yes. But not quite. Take a look at this;

NSMutableArray *list = [@[] mutableCopy];

This creates a non-mutable array @[] and calls mutableCopy which returns a NSMutableArray *. In place of @[], you can give any array literal.

回答5:

If you have a nested literal of arrays and dictionaries, you can turn this into a fully mutable version by going through NSJSONSerialization. For example:

NSArray* array = @[ @{ @"call" : @{ @"devices" : @[ @"$(devices)" ] } } ];
NSData* data   = [NSJSONSerialization dataWithJSONObject:array 
                                                 options:0 
                                                   error:nil];

NSJSONReadingOptions options = NSJSONReadingMutableContainers | 
                               NSJSONReadingMutableLeaves;
NSMutableArray* mutableArray = [NSJSONSerialization JSONObjectWithData:data 
                                                               options:options
                                                                 error:nil];

It's a bit of a detour, but at least you don't have to write out the code yourself. And the good thing is that NSJSONSerialization is very fast.