Question

I have seen in some source code (by other developers) something like this:

#import "SomeClass+SomeOtherClass.h"

What is the + for? What does this mean?

Answer 1

Let’s say you want to add functionality to an existing class (exp: NSString). You can do that by creating a subclass or you can use a category. And it is common to name the file where the category is defined using the pattern : MyClass+MyCategory.h.

For example, we can add a method reverseString to the class NSString in a category:

// File NSString+reversable.h
- (NSString *)reverseString;

// File NSString+reversable.m
- (NSString *)reverseString
{
    // Implementation
}

Have a look at this documentation for more information about categories.

Then you can use that category in another class:

#import "NSString+reversable.h"
// ...

NSString *aString = @"Hello!";
NSString *reversedString = [aString reverseString];