objective-c - self == [APLEvent class]有意思吗?

Question

#import "APLEvent.h"
#import "APLPhoto.h"

#import "APLImageToDataTransformer.h"

@implementation APLEvent

@dynamic creationDate, latitude, longitude, thumbnail, photo;

+ (void)initialize {
    if (self == [APLEvent class]) {
        APLImageToDataTransformer *transformer = [[APLImageToDataTransformer alloc] init];
        [NSValueTransformer setValueTransformer:transformer forName:@"APLImageToDataTransformer"];
    }
}

@end