Cocos2 code structure question

Question

I am doing tutorials to learn Cocos2d and have a question. here is the .m code:

#import "SceneManager.h"

@interface SceneManager ()
   +(void) go: (CCLayer *) layer;
   +(CCScene *) wrap: (CCLayer *) layer;
@end


@implementation SceneManager

    +(void) goPlay {
        CCLayer *layer = [PlayLayer node];
        [SceneManager go: layer];
}

+(void) go: (CCLayer *) layer {
    CCDirector *director = [CCDirector sharedDirector];
    CCScene *newScene = [SceneManager wrap:layer];

//    Class transition = nextTransition();

    if ([director runningScene]) {
         [director replaceScene:newScene];
}else {
    [director runWithScene:newScene];
}
}

+(CCScene *)wrap: (CCLayer *) layer {
    CCScene *newScene = [CCScene node];
    [newScene addChild: layer];
    return newScene;
}

@end

My question is why is there an @interface placed in the .m file and not included in the .h file?

Answer 1

That @interface Class () placed in the implementation file is a class extension to the SceneManager class which defines its private interface.

It's being used because go and wrap are only used by the implementation of this class and nowhere else (i.e. it's a private interface).

The @private modifier only works on variables, not on methods, so this is the way to hide them.

(Source: stackoverflow)