What is a better practice when defining a const NSString object in objective-c?

Question

When i read colleagues\' code in my team, i usually found there were two different types of definition for const NSString objects:

static NSString const *

Answer 1

NSString const *str

means str is immutable.if you change str value for example str=str2, there's error occurs.

NSString *const str

means what str point to is immutable.You can change str = str2;

since NSString is immutable

NSString *const str 

is equal to

NSString *str