gistfile1.txt

Resource.h
----------
@interface Resource : NSObject
+ (void)save:(NSError **)error;
@end

Resource.m
----------
@implementation Resource
+ (void)save:(NSError **)error {
    //do soething
}
@end

QuestionResource.h
------------------
#import "Resource.h"

@interface : Resource 
@end

QuestionResource.m
------------------
@implementation
@end

ExampleViewController.m
-----------------------
#import  "QuestionResource.h"

QuestionResource q = [[QuestionResource alloc] init];
NSError *error = nil;
[q save:&error];