I'm new into Obj-C.
I would like to know will there be any problems if I assigning NSMutableArray to NSArray as like example code below:
NSMutableArray *mutableArray = [NSMutableArray arrayWithObjects:@"item1", @"item2", nil];
NSArray *array = mutableArray;
I know that if i use [mutableArray copy] it will duplicate the array as new set. My question is will my approach conflict with any guidance or will have any problems?
Thanks.
Both pointers will refer to the same object. The nature and behavior of that object will remain the same. It is not aware nor affected by which pointers refer to it.
If the array is mutated, those mutations will be observable regardless of which pointer you use to message or examine the array.
The compiler will complain if methods present in NSMutableArray but not NSArray are sent via the array pointer. However, if you ignore the compiler's complaints, the methods will still work as normal. The static types of the pointers is only significant at compile time. They are not represented in the compiled program (except, possibly, in debugging information, but that doesn't affect runtime behavior).
NSString* foo = (NSString*)mutableArray. You've told the compiler that the pointer points to an NSString when it actually points to an NSMutableArray. If you then send foo messages that NSMutableArray implements, they will work as normal. The compiler will complain for methods that NSString doesn't declare (e.g. -count) but not for those it does (e.g. -description). Sending -length will cause an exception.The catch is this:
if mutableArray changed somehow, and the array still think of it self immutable.
Then, things might get out of control.
Other than this, I don't see much problem here...
Your array will stay mutable, but compiler will think that it is immutable. So it won't allow you to use methods specific for NSMutableArray without typecasting.
[myArray performSelector:@selector(removeAllObjects)]; . Assigning NSMutableArray to NSArray will not change object.