OC中的静态成员变量

#import <Foundation/Foundation.h>
#import "MyObject.h"

int main(int argc, const char * argv[]) {
    @autoreleasepool {
        [MyObject setFlag:YES];
        NSLog(@"%@", [MyObject flag] ? @"YES" : @"NO");
    }
    return 0;
}

#import <Foundation/Foundation.h>

@interface MyObject : NSObject

+ (BOOL)flag;
+ (void)setFlag:(BOOL)flag;

@end

#import "MyObject.h"

static BOOL _flag;

@implementation MyObject

+ (BOOL)flag {
    return _flag;
}

+ (void)setFlag:(BOOL)flag {
    _flag = flag;
}

@end

YES