How to initialize NSString for NSMutableString?

Question

Is there a way to initialize an NSString for an NSMutableString? as well as the reverse order?

-(void)st:(NSString *)st { NSMutableString str = st; // gives warning.. NSLog(@"string: %@", str); } 

Answer 1

NSString is an immutable view (or, in the worst case, readonly view). Thus, you will need to either switch to NSMutableString if you know that it is modified or make a mutable copy:

 -(void)st:(NSString *)st { NSMutableString *str = [[st mutableCopy] autorelease]; NSLog(@"string: %@", str); } 

I will implement it because mutableCopy returns a new initialized copy, keeping the number at 1.

Answer 2

You can set NSMutableString to NSString, but not vice versa.

 NSString *str = [NSMutableString alloc]init]; 

ok but

 NSMutableString *str = [[NSString alloc]init]; 

not. This is because NSMutableString is a subclass of NSString, so it is an "NSString". However, you can create a mutable string from NSString with

 NSMutableString *mStr = [str mutableCopy]; 

Answer 3

 NSString *someImmutableString = @"something"; NSMutableString *mutableString = [someImmutableString mutableCopy]; 

Important! mutableCopy returns the object you have, so you must either free it or auto-update it.

Answer 4

Swift 2.0

For Swift users, the following works in Xcode 7.

 var str : String = "Regular string" var mutableStr : NSMutableString = NSMutableString(string: str)