Venmo Objective-C Style Guide

This style guide outlines the coding conventions of the iOS team at Venmo. It was forked from the NYT iOS Style Guide.

Thanks to all of its contributors.

Introduction

Here are some of the documents from Apple that informed the style guide. If something isn't mentioned here, it's probably covered in great detail in one of these:

• The Objective-C Programming Language
• Cocoa Fundamentals Guide
• Coding Guidelines for Cocoa
• iOS App Programming Guide

Table of Contents

• Commits
• Dot-Notation Syntax
• Spacing
• Conditionals
  • Ternary Operator
• Error handling
• Methods
• Variables
• Naming
  • Constants and Enums
  • Underscores
• Compile-time Strings
• Comments
• Init & Dealloc
• Literals
• CGRect Functions
• Constants
• Enumerated Types
• Bitmasks
• Private Properties
• Image Naming
• Booleans
• Singletons
• Imports
• Xcode Project

Commits

Code should be commited granularly such that each commit represents a small unit of work that compiles and is in a functional state. Avoid commits where compiling is impossible unless it is necessary due to a large refactor.

Commits should have a short, descriptive message in the imperative mood as if commmanding the codebase to transform itself in such a way that the command is completed. e.g. Add support for multiple recipients on a payment or Fix bug where user is charged instead of paid if there are special characters in the to field.

Dot-Notation Syntax

Dot-notation should always be used for accessing and mutating properties. Bracket notation is preferred in all other instances.

For example:

view.backgroundColor = [UIColor orangeColor];
[UIApplication sharedApplication].delegate;

Not:

[view setBackgroundColor:[UIColor orangeColor]];
UIApplication.sharedApplication.delegate;

Spacing

• Indent using 4 spaces. Never indent with tabs. Be sure to set this preference in Xcode.
• Method braces should open on the next line and close on a new line. Other braces (if/else/switch/while etc.) always open on the same line as the statement but close on a new line.

For example:

- (void)doSomethingForUser
{
  if (user.isHappy) {
      // Do something
  } else {
      // Do something else
  }
}

• There should be exactly one blank line between methods, and two blank lines before a pragma mark. Whitespace within methods should separate functionality, but often there should probably be new methods.
• @synthesize and @dynamic should each be declared on new lines in the implementation.

Conditionals

Conditional bodies should always use braces even when a conditional body could be written without braces (e.g., it is one line only) to prevent errors. These errors include adding a second line and expecting it to be part of the if-statement. Another, even more dangerous defect may happen where the line "inside" the if-statement is commented out, and the next line unwittingly becomes part of the if-statement. In addition, this style is more consistent with all other conditionals, and therefore more easily scannable.

For example:

if (!error) {
    return success;
}

Not:

if (!error)
    return success;

or

if (!error) return success;

Multiline conditionals should break on the boolean operator, and the bracket should open on a new line to aid in readability.

For example:

if ((something &&
    somethingElse) ||
    anotherThing)
{
    // Do Stuff
}

Not:

if ((something &&
    somethingElse) ||
    anotherThing) {
    // Do Stuff
}

if ((something
    && somethingElse)
    || anotherThing)
{
    // Do Stuff
}

Ternary Operator

The Ternary operator, ? , should only be used when it increases clarity or code neatness. A single condition is usually all that should be evaluated. Evaluating multiple conditions is usually more understandable as an if statement, or refactored into instance variables.

For example:

result = a > b ? x : y;

Not:

result = a > b ? x = c > d ? c : d : y;

Null-coalescing operator

The null-coalescing operator, ?:, should be used instead of a repetitive ternary operator.

For example:

result = foo.name ?: @"";

Not:

result = foo.name ? foo.name : @"";

Error handling

When methods return an error parameter by reference, switch on the returned value, not the error variable.

For example:

NSError *error;
if (![self trySomethingWithError:&error]) {
    // Handle Error
}

Not:

NSError *error;
[self trySomethingWithError:&error];
if (error) {
    // Handle Error
}

Some of Apple’s APIs write garbage values to the error parameter (if non-NULL) in successful cases, so switching on the error can cause false negatives (and subsequently crash).

Methods

In method signatures, there should be a space after the scope (-/+ symbol). There should be a space between the method segments.

For Example:

- (void)setExampleText:(NSString *)text image:(UIImage *)image;

Variables

Variables should be named as descriptively as possible. Single letter variable names should be avoided except in for() loops.

Asterisks indicating pointers belong with the variable, e.g., NSString *text not NSString* text or NSString * text, except in the case of constants.

Property definitions should be used in place of naked instance variables whenever possible. Direct instance variable access should be avoided except in initializer methods (init, initWithCoder:, etc…), dealloc methods and within custom setters and getters. For more information on using Accessor Methods in Initializer Methods and dealloc, see here.

For example:

@interface NYTSection: NSObject

@property (nonatomic) NSString *headline;

@end

Not:

@interface NYTSection : NSObject {
    NSString *headline;
}

Variable Qualifiers

When it comes to the variable qualifiers introduced with ARC, the qualifier (__strong, __weak, __unsafe_unretained, __autoreleasing) should be placed between the asterisks and the variable name, e.g., NSString * __weak text.

Naming

Apple naming conventions should be adhered to wherever possible, especially those related to memory management rules (NARC).

Long, descriptive method and variable names are good.

For example:

UIButton *settingsButton;

Not

UIButton *setBut;

A three letter prefix (e.g. VEN) should always be used for class names and constants, however may be omitted for Core Data entity names. Constants should be camel-case with all words capitalized and prefixed by the related class name for clarity.

For example:

static const NSTimeInterval NYTArticleViewControllerNavigationFadeAnimationDuration = 0.3;

Not:

static const NSTimeInterval fadetime = 1.7;

Properties and local variables should be camel-case with the leading word being lowercase.

Instance variables should be camel-case with the leading word being lowercase, and should be prefixed with an underscore. This is consistent with instance variables synthesized automatically by LLVM. If LLVM can synthesize the variable automatically, then let it.

For example:

@synthesize descriptiveVariableName = _descriptiveVariableName;

Not:

id varnm;

Constants and Enums

Constants and enums should be descriptively named in order of increasing specificity:

NSString *const VENUserKeyHasLoggedIn = @"HasLoggedIn";
NSString *const VENUserKeyHasInvitedFriends = @"HasInvitedFriends";

typedef NS_ENUM(NSUInteger, VENPeopleDrawerSection) {
    VENPeopleDrawerSectionNearby,
    VENPeopleDrawerSectionRecents
};

Enums should start at 0 (the default for NS_ENUM) unless there is good reason not to (ie, not wanting the first value to match with nil)

Names should follow this form:

<constant-name> ::= "VEN" <category> <type> <name>
<type> ::= "Key" | "Name" | "Value" | "Parameter" | ""

Compile-time Strings

Prefer compile-time Strings over hardcoded strings:

For example:

[NSEntityDescription insertNewObjectForEntityForName:NSStringFromClass(User) inManagedObjectContext:context];
[NSPredicate predicateWithFormat:@"%K == %@", @keypath([User new], firstName), @"Eli"]

Not

[NSEntityDescription insertNewObjectForEntityForName:@"User" inManagedObjectContext:context];

Underscores

When using properties, instance variables should always be accessed and mutated using self.. This means that all properties will be visually distinct, as they will all be prefaced with self.. Local variables should not contain underscores.

Comments

Comments should always have a space after the //

For example:

// Good and fun looking


//Bad and harder to read

When they are needed, comments should be used to explain why a particular piece of code does something. Any comments that are used must be kept up-to-date or deleted.

Block comments should generally be avoided, as code should be as self-documenting as possible, with only the need for intermittent, few-line explanations. This does not apply to those comments used to generate documentation.

init and dealloc

dealloc methods should be placed at the top of the implementation, directly after the @synthesize and @dynamic statements. init should be placed directly below the dealloc methods of any class.

init methods should be structured like this:

- (instancetype)init
{
    self = [super init]; // or call the designated initializer
    if (self) {
        // Custom initialization
    }

    return self;
}

Literals

NSString, NSDictionary, NSArray, and NSNumber literals should be used whenever creating immutable instances of those objects. Pay special care that nil values not be passed into NSArray and NSDictionary literals, as this will cause a crash.

For example:

NSArray *names = @[@"Brian", @"Matt", @"Chris", @"Alex", @"Steve", @"Paul"];
NSDictionary *productManagers = @{@"iPhone" : @"Kate", @"iPad" : @"Kamal", @"Mobile Web" : @"Bill"};
NSNumber *shouldUseLiterals = @YES;
NSNumber *buildingZIPCode = @10018;

Not:

NSArray *names = [NSArray arrayWithObjects:@"Brian", @"Matt", @"Chris", @"Alex", @"Steve", @"Paul", nil];
NSDictionary *productManagers = [NSDictionary dictionaryWithObjectsAndKeys: @"Kate", @"iPhone", @"Kamal", @"iPad", @"Bill", @"Mobile Web", nil];
NSNumber *shouldUseLiterals = [NSNumber numberWithBool:YES];
NSNumber *buildingZIPCode = [NSNumber numberWithInteger:10018];

CGRect Functions

When accessing the x, y, width, or height of a CGRect, always use the CGGeometry functions instead of direct struct member access. From Apple's CGGeometry reference:

All functions described in this reference that take CGRect data structures as inputs implicitly standardize those rectangles before calculating their results. For this reason, your applications should avoid directly reading and writing the data stored in the CGRect data structure. Instead, use the functions described here to manipulate rectangles and to retrieve their characteristics.

For example:

CGRect frame = self.view.frame;

CGFloat x = CGRectGetMinX(frame);
CGFloat y = CGRectGetMinY(frame);
CGFloat width = CGRectGetWidth(frame);
CGFloat height = CGRectGetHeight(frame);

Not:

CGRect frame = self.view.frame;

CGFloat x = frame.origin.x;
CGFloat y = frame.origin.y;
CGFloat width = frame.size.width;
CGFloat height = frame.size.height;

Constants

Constants are preferred over in-line string literals or numbers, as they allow for easy reproduction of commonly used variables and can be quickly changed without the need for find and replace. Constants should be declared as static constants and not #defines unless explicitly being used as a macro.

For example:

static NSString * const NYTAboutViewControllerCompanyName = @"The New York Times Company";

static const CGFloat NYTImageThumbnailHeight = 50.0;

Not:

#define CompanyName @"The New York Times Company"

#define thumbnailHeight 2

Enumerated Types

When using enums, it is recommended to use the new fixed underlying type specification because it has stronger type checking and code completion. The SDK now includes a macro to facilitate and encourage use of fixed underlying types — NS_ENUM()

Example:

typedef NS_ENUM(NSInteger, NYTAdRequestState) {
    NYTAdRequestStateInactive,
    NYTAdRequestStateLoading
};

Bitmasks

When working with bitmasks, use the NS_OPTIONS macro.

Example:

typedef NS_OPTIONS(NSUInteger, NYTAdCategory) {
  NYTAdCategoryAutos      = 1 << 0,
  NYTAdCategoryJobs       = 1 << 1,
  NYTAdCategoryRealState  = 1 << 2,
  NYTAdCategoryTechnology = 1 << 3
};

Private Properties

Private properties should be declared in class extensions (anonymous categories) in the implementation file of a class. Named categories (such as NYTPrivate or private) should never be used unless extending another class.

For example:

@interface NYTAdvertisement ()

@property (nonatomic, strong) GADBannerView *googleAdView;
@property (nonatomic, strong) ADBannerView *iAdView;
@property (nonatomic, strong) UIWebView *adXWebView;

@end

Image Naming

Image names should be named consistently to preserve organization and developer sanity. They should be named as one camel case string with a description of their purpose, followed by the un-prefixed name of the class or property they are customizing (if there is one), followed by a further description of color and/or placement, and finally their state.

For example:

• RefreshBarButtonItem / RefreshBarButtonItem@2x and RefreshBarButtonItemSelected / RefreshBarButtonItemSelected@2x
• ArticleNavigationBarWhite / ArticleNavigationBarWhite@2x and ArticleNavigationBarBlackSelected / ArticleNavigationBarBlackSelected@2x.

Images that are used for a similar purpose should be grouped in respective groups in an Images folder.

Booleans

Since nil resolves to NO it is unnecessary to compare it in conditions. Never compare something directly to YES, because YES is defined to 1 and a BOOL can be up to 8 bits.

This allows for more consistency across files and greater visual clarity.

For example:

if (!someObject) {
}

Not:

if (someObject == nil) {
}

---

For a BOOL, here are two examples:

if (isAwesome)
if (![someObject boolValue])

Not:

if (isAwesome == YES) // Never do this.
if ([someObject boolValue] == NO)
if (isAwesome == YES) // Never do this.

---

If the name of a BOOL property is expressed as an adjective, the property can omit the “is” prefix but specifies the conventional name for the get accessor, for example:

@property (assign, getter=isEditable) BOOL editable;

Text and example taken from the Cocoa Naming Guidelines.

Singletons

Singleton objects should use a thread-safe pattern for creating their shared instance, GCD dispatch_once is preferred over the older @synchronized method.

+ (instancetype)sharedInstance {
   static id sharedInstance = nil;

   static dispatch_once_t onceToken;
   dispatch_once(&onceToken, ^{
      sharedInstance = [[self alloc] init];
   });

   return sharedInstance;
}

This will prevent possible and sometimes prolific crashes.

Resources

Resources should be grouped in folders under the Resources folder which map to the functional area of the app.

Resource names should be prepended with the name of the functional area and an underscore (e.g. SideDrawer_Icon or PaymentFeed_BackgroundGradient) and should be written in camel case. All image resources should have both a retina (@2x) and non-retina version. The non-retina version should be the exact pixel size of the UIImageView that it's contained within.

e.g. SideDrawer_HeaderSeparator.png and SideDrawer_HeaderSeparator@2x.png

NOT any of...

side_drawer_header_separator.png
headerSeparator.png
separator.png
etc..

Xcode project

The physical files should be kept in sync with the Xcode project files in order to avoid file sprawl. Any Xcode groups created should be reflected by folders in the filesystem. Code should be grouped not only by type, but also by feature for greater clarity.

When possible, always turn on "Treat Warnings as Errors" in the target's Build Settings and enable as many additional warnings as possible. If you need to ignore a specific warning, use Clang's pragma feature.

Imports

If there is more than one import statement, group the statements together. Commenting each group is optional.

Note: For modules use the @import syntax.

// Frameworks
@import QuartzCore;

// Models
#import "NYTUser.h"

// Views
#import "NYTButton.h"
#import "NYTUserView.h"

Blocks

When using blocks, you MUST make sure that the block exists and is valid before executing it. ARC does not nil blocks whose scope is no longer relevant.

if (blockName) {
  blockName(arg1, arg2);
}

Not..

blockName(arg1, arg2); // EXC_BAD_ACCESS if it's owner has been released

Podfile

Podfiles should explicitly call out targets which the pods should be included in and explicitly state the minimum OS version for each.

inhibit_all_warnings!

target 'Venmo', :exclusive => true do
  platform :ios, '6.0'
  pod 'Underscore.m', '~> 0.2'
end

target 'Regression Tests', :exclusive => true do
  platform :ios, '6.0'
  pod 'Specta', '~> 0.2.1'
  pod 'Expecta', '~> 0.2.2'
end

The inhibit_all_warnings! property should be set to ensure that we can target 0-warnings in our builds. Where we created a pod internally, it should have 'treat warnings as errors' enabled so should not trigger warnings.

Pods should specify an explicit version and allow hotfix-level updates using the ~> indicator.

Other Objective-C Style Guides

If ours doesn't fit your tastes, have a look at some other style guides:

• Google
• GitHub
• Adium
• Sam Soffes
• CocoaDevCentral
• Luke Redpath
• Marcus Zarra