#import <Foundation/Foundation.h>

@interface FKFruit : NSObject

@property(nonatomic, assign) double weight;
@property(nonatomic, assign) int a;

-(void) info;
@end

@implementation FKFruit

-(void)info
{
    NSLog(@"Fruit!!!, weight: %f, a: %d", _weight, self.a);
}

-(void)setA:(int)aa
{
    _a = aa; //这样为什么正确
//    self.a = aa; //这样为什么错误
}


@end


@interface FKApple : FKFruit

@end

@implementation FKApple

-(void)info
{
    [super info];
    NSLog(@"Apple");
}

@end

int main (int argc, char * argv[])
{
    @autoreleasepool {
        FKApple * apple = [[FKApple alloc] init];
        apple.weight = 100;
        apple.a = 1009;
        [apple info];
    }
}




clang -fobjc-arc -framework Foundation propery.m