Objective-C 101 (retain vs assign) NSString

user_138260 0
Viewed 66542

A 101 question

Let's say i'm making database of cars and each car object is defined as:

#import <UIKit/UIKit.h>

@interface Car:NSObject{
    NSString *name;
}

@property(nonatomic, retain) NSString *name;

Why is it @property(nonatomic, retain) NSString *name; and not @property(nonatomic, assign) NSString *name;?

I understand that assign will not increment the reference counter as retain will do. But why use retain, since name is a member of the todo object the scope of it is to itself.

No other external function will modify it either.

retain nsstring objective-c iphone ios
8 Answers

and don't forget to access it via

self.name = something;

because

name = something;

will not care about the generated setter/getter methods but instead assign the value directly.

user_5221020

For those who are looking for it, Apple's documentation on property attributes is here.

user_5341200

Google's Objective-C Style Guide covers this pretty well:

Setters taking an NSString, should always copy the string it accepts. Never just retain the string. This avoids the caller changing it under you without your knowledge. Don't assume that because you're accepting an NSString that it's not actually an NSMutableString.

user_8789690

Would it be unfortunate if your class got this string object and it then disappeared out from under it? You know, like the second time your class mentions that object, it's been dealloc'ed by another object?

That's why you want to use the retain setter semantics.

user_3354150
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