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What do the plus and minus signs mean in Objective C next to a method?
As I continue to learn about iOS, I came across this, +(CCScene *)function {...} in an early line of the example code I was working with. I understand that methods are implemented inObj-C with a -, as in the following method: -(ObjectType*)function {...}, but I am curious, what does the + that precedes the apparent function implementation indicate?
Instance methods (or rather messages in Objective-C) start with a -. Class methods start with a +. The difference is, that instance messages can be sent to objects of a certain class, while class messages has be sent to the class itself.
Let's say you have a class called Country. Then you might have an instance message name or area, which will return the name or the area of your Country instance.
NSString *name = [someCountry name];
// name could be "Germany" or "France" for instance.
You might also have a numberOfCountries class message, which will return the total number of Country instances.
int totalCount = [Country numberOfCountries];
'+' indicates a class method and '-' indicates an instance method. Thus, +(CCScene *)function {...} is a class method.
Instance methods operate on an object and has access to its instance variables, while a class method operates on a class as a whole and has no access to a particular instance's variables (unless you pass the instance in as a parameter).
For more information, see "Class vs Instance Methods?" here on Stackoverflow.
