Objective-C Method Types

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Objective-C Method Types

+7 A:

A minus signifies an object instance method, a plus signifies a class method - known in other languages as a 'static method'.

More info on method types can be found in this wikipedia article.

teabot 2009-07-10 09:12:24

Ok, so if I understand this correctly, I would create a new instance of the array object and use the minus sign?When would I find myself using the plus sign with an array then. Surely I always have to create an instance of an array to use one?

JonB 2009-07-10 09:13:58

Using NSArray as an example, you might call the class method [NSArray arrayWithObject:] to create an instance of NSArray containing the object you pass in.

teabot 2009-07-10 09:16:55

As i understand it, those are for the function definitions. if one is defined with a plus then you call it through the class. Otherwise, you call it through an instance.

RCIX 2009-07-10 09:16:56

an example may be the best way to clarify this: [NSMutableArray arrayWithCapacity:10] and [[[NSMutableArray alloc] initWithCapacity:10] autorelease] are equivalent, one is "+ arrayWithCapacity:" the other is "-initWithCapacity:"

cobbal 2009-07-10 09:18:09

Just to clarify, I understand what a static method is. I just can't see why there would need to be one for an Array, when surely every-time you have to create an instance of an Array to use one?

JonB 2009-07-10 09:18:50

Ah, so it allows you to create an array without having to make the instance first. You still get given an array object at the end of it. Makes sense.

JonB 2009-07-10 09:20:21

Thanks for your help all.

JonB 2009-07-10 09:24:06

@JonB: Exactly, it's actually a factory method. Note however that those factory methods return autoreleased instances, whereas instances created viaalloc/init have to be released manually. This is a common (and hard to debug) memory management mistake.

Daniel Rinser 2009-07-10 13:47:26

@Daniel is correct that +arrayWith... methods are factory methods (in Objective-C we generally call static methods with this functionality "convenience constructors"), but of course not all static methods are or must be. For example, NSURLProtocol is an abstract class with a number of static utility methods.

Quinn Taylor 2009-07-10 14:51:30

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