I always use underscores. It creates a clear distinction between local variables and instance variables. It also avoids compiler warnings in the following situation:
@interface MyClass
{
NSString *name
}
@property (nonatomic, copy) NSString *name;
- (id) initWithName:(NSString *) name;
@end
@implementation MyClass
@synthesize name;
// The following method will result in a compiler warning
// (parameter name same as ivar name)
- (id) initWithName:(NSString *) name {
if (self = [super init]) {
self.name = name;
}
return self;
}
@end
EDIT:
After having to endure downvotes and reading through the comments, let me try to make my point:
Apple recommends that ivars have the same name as their property. Apple also recommends that properties start with a lowercase letter. And Apple also recommends that local variables start with a lowercase letter.
Now you have a problem, because when you read a piece of code, and you see a variable being used, you cant’ tell by the naming convention if this variable is an ivar or a local variable. That sucks. The solution is to have different naming conventions for ivars and local variables. That’s just plain common sense.
The way you implement this naming convention is irrelevant. If you really want, you can simply append “_WOOHAHA” to the ivar names. I don’t care (but maybe others will). The thing is that people who know what they’re doing have decided to go with the “underscore prefix” for ivars. IMHO, they made the right decision, even if their own company recommends something else. (the developers I’m talking about are the people writing some major Apple frameworks and the .NET Framework classes)
In the end, code quality is more important than following a stupid rule that isn’t even followed by the people preaching it.
Another remark about the code you’ve shown: never use retain on string properties. You should use copy instead.
For more info about copy/retain on properties, see: