NSMutableArray automatically typecasting into NSArray

Question

I created an NSMutableArray object by

NSMutableArray *array = [[NSMutableArray alloc]init];

and used method componentsSeperatedByString: as

array = [myString componentsSeperatedByString:@"++"];

but when I performed operation on array like,

[array removeAllObjects];

I got exception like "removeAllObjects unrecognized selector send to instance".

I solved this issue by modifying code like,

NSArray *components = [myString componentsSeperatedByString:@"++"];



array = [NSMutableArray arrayWithArray:components];

and I after that could perform operation like

[array removeAllObjects];

My doubt is why did NSMutableArray automaticaqlly converted to NSArray? How Can I avoid automatic type conversion like this, to prevent exceptions? Thanks in advance....

Answer 1

There is a mistake in your understanding of how Objective-C works. This line:

NSMutableArray *array = [[NSMutableArray alloc]init];

allocates and initializes the array, and the pointer array points to this object. Now, this line:

array = [myString componentsSeperatedByString:@"++"];

makes the array pointer to point to the new array returned by componentsSeparatedByString method. You loose the reference to your alloced and inited mutable array when you do this, and you create the memory leak if you don't use ARC.

Answer 2

This is happening because [myString componentsSeperatedByString:@"++"] returns an NSArray. You can try something like this:

array = [[myString componentsSeperatedByString:@"++"] mutableCopy];

or

array = [NSMutableArray arrayWithArray:[myString componentsSeperatedByString:@"++"]];