Swizzle UserDefaults set(object: forKey:) in objc and swift

UserDefaults+Swizzle.swift

/// ObjC
@implementation NSUserDefaults(Tracking)

+ (void)load {

    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        Class class = [self class];

        SEL originalSelector = @selector(setObject:forKey:);
        SEL swizzledSelector = @selector(swizzledSetObject:forKey:);

        Method originalMethod = class_getInstanceMethod(class, originalSelector);
        Method swizzledMethod = class_getInstanceMethod(class, swizzledSelector);

        IMP originalImp = method_getImplementation(originalMethod);
        IMP swizzledImp = method_getImplementation(swizzledMethod);

        class_replaceMethod(class,
                swizzledSelector,
                originalImp,
                method_getTypeEncoding(originalMethod));
        class_replaceMethod(class,
                originalSelector,
                swizzledImp,
                method_getTypeEncoding(swizzledSelector));

    });
}

- (void) swizzledSetObject: (nullable id) object forKey: (nonnull NSString *) key {
    [self swizzledSetObject:object forKey:key];
    if ([key isEqualToString:@"trackedPropertyKey"]) {
        NSLog(@"SwizzledSetObject %@ object: %@", key, object);
    }
}

@end

// Swift

extension UserDefaults {

    static let classInit: Void = {
        let setObjectSelector = #selector(NSMutableDictionary.setObject(_:forKey:)) // or NSSelectorFromString("setObject:forKey:")

        let setObjectMethod = class_getInstanceMethod(UserDefaults.self, setObjectSelector)

        let setObjectSwizzledMethod = class_getInstanceMethod(UserDefaults.self, #selector(swizzleSet(_:forKey:)))
        guard
            let originalMethod = setObjectMethod,
            let swizzledMethod = setObjectSwizzledMethod else
        {
            return
        }
        method_exchangeImplementations(originalMethod, swizzledMethod)
    }()

    @objc
    func swizzleSet(_ value: Any?, forKey defaultName: String) {
        swizzleSet(value, forKey: defaultName)
        if
            defaultName == "trackedPropertyKey" {
            print("swizzleSet", defaultName, value)
        }
    }
}