Google Objective-C Style Guide

Official Google Objective-C coding standards for consistent iOS/macOS code.

Golden Rules

1. Use ARC — Automatic Reference Counting (no manual retain/release)
2. Descriptive naming — clarity over brevity; method names read like sentences
3. Prefix class names — avoid namespace collisions (2-3 letter prefix)
4. Use properties — prefer @property over direct instance variables
5. Nullability annotations — mark nullable/nonnull on APIs
6. Use modern Objective-C — literals, subscripting, generics
7. Follow Apple conventions — consistency with Cocoa frameworks

Quick Reference

Naming Conventions

Class Interface

// ✓ CORRECT - class interface with nullability and generics
@interface GTMUserService : NSObject

@property(nonatomic, readonly) NSInteger userCount;
@property(nonatomic, copy, nullable) NSString *currentUserName;

- (nullable GTMUser *)userWithId:(NSInteger)userId;
- (void)fetchUsersWithCompletion:(void (^)(NSArray<GTMUser *> *_Nullable users,
                                          NSError *_Nullable error))completion;
@end

Properties

// ✓ CORRECT - property declarations
@property(nonatomic, strong) NSMutableArray<GTMUser *> *users;
@property(nonatomic, copy) NSString *title;
@property(nonatomic, assign) BOOL isLoading;
@property(nonatomic, weak) id<GTMUserDelegate> delegate;
@property(nonatomic, readonly) NSInteger count;

// Attribute order: nonatomic/atomic, memory (strong/weak/copy/assign),
// then access (readonly/readwrite)

Methods

// ✓ CORRECT - descriptive method names (reads like a sentence)
- (nullable GTMUser *)userWithFirstName:(NSString *)firstName
                               lastName:(NSString *)lastName;

// ✓ CORRECT - instance method
- (void)setUser:(GTMUser *)user forKey:(NSString *)key;

// ✓ CORRECT - class method (factory)
+ (instancetype)serviceWithBaseURL:(NSURL *)baseURL;

// ✗ INCORRECT - too abbreviated
- (GTMUser *)usr:(NSString *)fn ln:(NSString *)ln;

Modern Objective-C Literals

// ✓ CORRECT - use modern literals
NSArray *colors = @[@"red", @"green", @"blue"];
NSDictionary *config = @{@"host": @"localhost", @"port": @8080};
NSNumber *count = @42;
NSNumber *enabled = @YES;

// ✓ CORRECT - subscripting
NSString *first = colors[0];
NSString *host = config[@"host"];

// ✗ INCORRECT - old style
NSArray *colors = [NSArray arrayWithObjects:@"red", @"green", nil];

Protocols and Delegates

// ✓ CORRECT - optional and required protocol methods
@protocol GTMUserServiceDelegate <NSObject>

@required
- (void)userService:(GTMUserService *)service
    didLoadUser:(GTMUser *)user;

@optional
- (void)userService:(GTMUserService *)service
    didFailWithError:(NSError *)error;

@end

Memory Management with ARC

// ✓ CORRECT - ARC handles retain/release
@implementation GTMUserService {
  NSMutableArray<GTMUser *> *_users;  // strong by default
}

- (instancetype)init {
  self = [super init];
  if (self) {
    _users = [[NSMutableArray alloc] init];
  }
  return self;
}
@end

// ✓ CORRECT - weak references to avoid cycles
__weak typeof(self) weakSelf = self;
[self fetchData:^{
  __strong typeof(weakSelf) strongSelf = weakSelf;
  if (!strongSelf) return;
  [strongSelf processResults];
}];

Nullability Annotations

// ✓ CORRECT - annotate all APIs
NS_ASSUME_NONNULL_BEGIN

@interface GTMUser : NSObject

@property(nonatomic, copy) NSString *name;
@property(nonatomic, copy, nullable) NSString *email;

- (nullable GTMUser *)userWithId:(NSInteger)userId;

@end

NS_ASSUME_NONNULL_END

Common Mistakes

When to Use This Guide

• Writing new Objective-C code
• Maintaining legacy Objective-C iOS/macOS apps
• Code reviews
• Onboarding new team members

Install

npx skills add testdino-hq/google-styleguides-skills/objective-c

Full Guide

See objective-c.md for complete details, examples, and edge cases.