Question

As Objective-C has evolved (I use it exclusively with xcode/ios for iPhone/iPad development), there seems to be many different ways you can layout your class instance variables. Is there a ‘best practice’ way that’s become common consensus? (I realise Apple demo/example code is all over the place in terms of style)

In particular the idea of handling private variables. Here are a number of ways I’ve seen to manage some instance variables for a class (I’ve left out the interface/implementation for brevity) – and I’m not even including the use of underscore named synthesized properties.

.h

@property (nonatomic, strong) NSString *aString;

.m

@synthesize aString;

- (void)aMethod {
   aString = @"Access directly, but if I don't have custom getter/setters and am using ARC, do I care?";
   self.aString = @"Access through self";
}

Or this:

.h

@property (readonly) NSString *aString;

.m

@property (nonatomic, strong) NSString *aString;
...
@synthesize aString;

Or this:

.m

@interface aClass {
 NSString *aPrivateString;
}

- (void)aMethod {
  aPrivateString = @"Now I have to access directly, but is this atomic/nonatomic?";
}

I don’t want this question to turn into a style argument, but it seems to me there should be a “if you’re not doing something specific or complex or weird, use this method for defining your class variables” standard.

Answer 1

I’d prefer use the following convention for public and private ivars/properties:

.h

@property (nonatomic, strong) NSString *publicString;

.m

@implemention aClass 
{
  NSNumber *_privateNumber;
}
@synthesize publicString = _publicString;

This way everything starting with _ is an ivar (_publicString is the underlying ivar for the property, this prevents me from using publicString while I want to use self.publicString).