why does __block not adding values to array

Question

I am enumerating ranges inside a block and storing the values inside an array. I expected using __block should store the values inside block into array?

 __block  NSMutableArray *array;
  [indexSet enumerateRangesUsingBlock:^(NSRange range,BOOL * stop ) {

    [array addObject:@(range.location)];
    [array addObject:@(range.length)];

     NSLog(@"location is %d, %ld", range.location, range.length);


}];


NSLog(@"%@",array );

But this result in

location is 4, 2 location is 8, 2 location is 14, 2

and for array

(null)

I expected array to be filled with values.

The __block is not needed, even once you do allocate the array. — bbum
– bbum, Commented Apr 26, 2018 at 18:01

vadian · Accepted Answer · 2018-04-26 08:18:16Z

1

You have to initialize it, a just declared array is nil:

__block  NSMutableArray *array = [NSMutableArray array];

(The Swift compiler would throw an error ... 😉 )

answered Apr 26, 2018 at 8:18

vadian

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1 Comment

CRD Over a year ago

Vadian, you forgot to explain that the __block is redundant

humble_pie · Accepted Answer · 2018-04-27 06:33:24Z

0

__block NSMutableArray *array = [NSMutableArray array];

It does work fine.

However when I declared array as property then block became redundant.

answered Apr 27, 2018 at 6:33

humble_pie

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1 Comment

CRD Over a year ago

__block was always redundant. The attribute allows you to change the value of the variable array within your block, you are not doing that, it's value remains the same - it always references the same array. It is the mutable array whose content changes.

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