Objective-C 101 (retain vs assign) NSString

Question

A 101 question

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

#import 

@interface Car:NSObject{
            


        

Answer 1

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.

Answer 2

Without retain there is no guarantee the NSString* you are setting name with will live any longer than the assignment statement itself. By using the retain property for the synthesized setter you're allowing it to tell the memory management system that there is at least one more object interested in keeping the NSString* around.

Answer 3

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

Answer 4

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.

Answer 5

After reading so many Articles, SO posts and made demo apps to check Variable property attributes, I decided to put all the attributes information together

1. atomic //default
2. nonatomic
3. strong=retain //default
4. weak= unsafe_unretained
5. retain
6. assign //default
7. unsafe_unretained
8. copy
9. readonly
10. readwrite //default

so below is the detailed article link where you can find above mentioned all attributes, that will defiantly help you. Many thanks to all the people who give best answers here!!

Variable property attributes or Modifiers in iOS

1. retain = strong
   • it is retained, old value is released and it is assigned
   • retain specifies the new value should be sent -retain on assignment and the old value sent -release
   • retain is the same as strong.
   • apple says if you write retain it will auto converted/work like strong only.
   • methods like "alloc" include an implicit "retain"

Example:

@property (nonatomic, retain) NSString *name;

@synthesize name;

2. assign
   • assign is the default and simply performs a variable assignment
   • assign is a property attribute that tells the compiler how to synthesize the property's setter implementation
   • I would use assign for C primitive properties and weak for weak references to Objective-C objects.

Example:

@property (nonatomic, assign) NSString *address;

@synthesize address;

Answer 6

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.