Chromium Objective-C and Objective-C++ style guide

For other languages, please see the Chromium style guides.

Chromium follows the Google Objective-C style guide unless an exception is listed below.

A checkout should give you clang-format to automatically format Objective-C and Objective-C++ code. By policy, Clang‘s formatting of code should always be accepted in code reviews. If Clang’s formatting doesn't follow this style guide, file a bug.

Line length

For consistency with the 80 character line length used in Chromium C++ code, Objective-C and Objective-C++ code also has an 80 character line length.

Chromium C++ style

Where appropriate, the Chromium C++ style style guide applies to Chromium Objective-C and (especially) Objective-C++

Code Formatting

Use nil for null pointers to Objective-C objects, and nullptr for C++ objects.

Delineate interface implementations with #pragma mark -

To keep implementation files organized and navigable, method implementations should be clearly grouped by the interfaces they implement, and each such group should be marked with a #pragma mark -, followed by the interface name (see examples below). This kind of grouping should happen for the implementations‘s public methods, superclass methods, private methods, and each protocol the implementation conforms to. In each group, methods should appear in the same order they are defined in the corresponding interface declaration. (This is less important for superclass methods for UIKit subclasses; it’s not a big deal if the ordering of UIViewController subclass methods doesn't match the UIKit header).

@interface ExampleViewController : UIViewController<ExampleConsumer, 


@implementation ExampleViewController

- (instancetype)init {

#pragma mark - Public Properties

- (NSString*)stringProperty {

... // Other properties

#pragma mark - UIViewController

- (void)viewDidLoad {

... // Other superclass methods

#pragma mark - UITableViewDelegate

... // Protocol methods

#pragma mark - ExampleConsumer

... // Protocol methods

#pragma mark - Private methods

... // Private methods

Private methods can be grouped differently if it helps make the code more readable; for example, private methods that are just helpers for methods in specific protocols could be grouped under a #pragma mark - <Protocol> helpers, directly after the protocol methods, instead of with the other private methods.

Remember that any method which isn't declared in an interface needs a full method comment.

Objective-C++ style matches the language

Within an Objective-C++ source file, follow the style for the language of the function or method you're implementing.

In order to minimize clashes between the differing naming styles when mixing Cocoa/Objective-C and C++, follow the style of the method being implemented.

For code in an @implementation block, use the Objective-C naming rules. For code in a method of a C++ class, use the C++ naming rules.

For C functions and constants defined in a namespace, use C++ style, even if most of the file is Objective-C.

TEST and TEST_F macros expand to C++ methods, so even if a unit test is mostly testing Objective-C objects and methods, the test should be written using C++ style.

#import and #include in the ios/ directory

#import directive can be used to import C++ and Objective-C headers for all source code in the ios/ directory. This differs from the Google Objective-C Style Guide, which requires using #include directive for C++ headers.

Disambiguating Symbols

Where needed to avoid ambiguity, use backticks to quote variable names and symbols in comments in preference to using quotation marks or naming the symbols inline.

This is more specific than the Google Objective-C Style Guide which allows pipes or backticks.