Contributing to Project

Code of Conduct

This project and everyone participating in it is governed by the Code of Conduct. By participating, you are expected to uphold this code.

How Can I Contribute

Reporting Bugs

Before creating bug reports ensure the bug was not already reported by searching on GitHub under Issues. If you're unable to find an open issue addressing the problem, open a new one. Explain the problem and include additional details to help maintainers reproduce the problem:

Use a clear and descriptive title for the issue to identify the problem.
Describe the exact steps which reproduce the problem in as many details as possible.
Provide specific examples to demonstrate the steps. Include links to files or GitHub projects, or copy/pasteable snippets, which you use in those examples. If you're providing snippets in the issue, use Markdown code blocks.
Provide log entries of both OpenVPN client and server if possible to help maintainers address the problem.
Include details about your configuration and environment. The name and version of the OS you're using, client and server configuration, etc.

Suggesting Enhancements

Before creating enhancement suggestions, please check GitHub Issues as you might find out that you don't need to create one. When you are creating an enhancement suggestion, please include as many details as possible:

Use a clear and descriptive title for the issue to identify the suggestion.
Provide a step-by-step description of the suggested enhancement in as many details as possible.
Provide specific examples to demonstrate the steps. Include copy/pasteable snippets which you use in those examples, as Markdown code blocks.
Explain why this enhancement would be useful.

Pull Requests

Open a new GitHub pull request.
Ensure the PR description clearly describes the problem and solution. Include the relevant issue number if applicable.
Before submitting, please read the Style Guide to know more about coding conventions.

Style Guide

Based on Google Objective-C Style Guide and NYTimes Objective-C Style Guide

The purpose of this part is to describe the Objective-C (and Objective-C++) coding guidelines and practices that should be used for iOS and OS X code. Apple has already written a very good, and widely accepted, Cocoa Coding Guidelines for Objective-C. Please read it in addition to this guide.

Spacing and Formatting

Spaces vs. Tabs

Use only spaces, and indent 4 spaces at a time. We use spaces for indentation. Do not use tabs in your code.

Line Length

The maximum line length for Objective-C files is 125 columns. You can make violations easier to spot by enabling Preferences > Text Editing > Page guide at column: 125 in Xcode.

Conditionals

Include a space after if, while, for, and switch, and around comparison operators.

// GOOD:

for (int i = 0; i < 5; ++i) {
    ...
}

while (test) {
    ...
}

Conditional bodies MUST use braces even when a conditional body could be written without braces (e.g., it is one line only) to prevent errors.

// GOOD:

if (!error) { return success; }

// AVOID:

if (!error)
    return success;

if (!error) return success;

Ternary Operator

The intent of the ternary operator is to increase clarity or code neatness. The ternary SHOULD only evaluate a single condition per expression. Evaluating multiple conditions is usually more understandable as an if statement or refactored into named variables.

// GOOD:

result = a > b ? x : y;

// AVOID:

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

Expressions

Use a space around binary operators and assignments. Omit a space for a unary operator. Do not add spaces inside parentheses.

// GOOD:

x = 0;
v = w * x + y / z;
v = -y * (x + z);

Variables

Asterisks indicating a type is a pointer MUST be "attached to" the variable name or const keyword. For example, NSString *text or NSString *const NYTConstantString, not NSString* text or NSString * text.

When it comes to the variable qualifiers introduced with ARC, the qualifier (__strong, __weak, __unsafe_unretained, __autoreleasing) SHOULD be placed at the beginning of declaration, e.g., __weak NSString * text

Properties

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.

// GOOD:

@interface NYTSection: NSObject

@property (nonatomic, nullable) NSString *headline;

@end

// AVOID:

@interface NYTSection : NSObject {
    NSString *headline;
}

Dot notation is RECOMMENDED over bracket notation for getting and setting properties.

// GOOD:

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

// AVOID:

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

Method Declarations and Definitions

One space should be used between the - or + and the return type, and no spacing in the parameter list except between parameters.

Methods should look like this:

// GOOD:

- (void)doSomethingWithString:(NSString *)theString {
    ...
}

Asterisks indicating a type is a pointer MUST be "attached to" the argument name.

When it comes to the nullability specifiers, the specifiers (nonnull, nullable, null_unspecified) SHOULD be placed immediately after an open parenthesis, as long as the type is a simple object or block pointer:

// GOOD:

- (void)doSomethingWithString:(nonnull NSString *)theString;

You can mark certain regions of your Objective-C header files as audited for nullability using NS_ASSUME_NONNULL_BEGIN and NS_ASSUME_NONNULL_END. Within these regions, any simple pointer type will be assumed to be nonnull.

// GOOD:

NS_ASSUME_NONNULL_BEGIN

@interface AAPLList : NSObject <NSCoding, NSCopying>

// ...

- (nullable AAPLListItem *)itemWithName:(NSString *)name;
- (NSInteger)indexOfItem:(AAPLListItem *)item;

@property (copy, nullable) NSString *name;
@property (copy, readonly) NSArray *allItems;

// ...

@end

NS_ASSUME_NONNULL_END

If you have too many parameters to fit on one line, giving each its own line is preferred. If multiple lines are used, align each using the colon before the parameter.

// GOOD:

- (void)doSomethingWithFoo:(GTMFoo *)theFoo
                      rect:(NSRect)theRect
                  interval:(float)theInterval {
    ...
}

When the second or later parameter name is longer than the first, indent the second and later lines by at least four spaces, maintaining colon alignment:

// GOOD:

- (void)short:(GTMFoo *)theFoo
          longKeyword:(NSRect)theRect
    evenLongerKeyword:(float)theInterval
                error:(NSError **)theError {
    ...
}

Method Invocations

Method invocations should be formatted much like method declarations. When there’s a choice of formatting styles, follow the convention already used in a given source file. Invocations should have all arguments on one line:

// GOOD:

[myObject doFooWith:arg1 name:arg2 error:arg3];

or have one argument per line, with colons aligned:

// GOOD:

[myObject doFooWith:arg1
               name:arg2
              error:arg3];

Don’t use any of these styles:

// AVOID:

[myObject doFooWith:arg1 name:arg2  // some lines with >1 arg
              error:arg3];

[myObject doFooWith:arg1
               name:arg2 error:arg3];

[myObject doFooWith:arg1
          name:arg2  // aligning keywords instead of colons
          error:arg3];

As with declarations and definitions, when the first keyword is shorter than the others, indent the later lines by at least four spaces, maintaining colon alignment:

// GOOD:

[myObj short:arg1
          longKeyword:arg2
    evenLongerKeyword:arg3
                error:arg4];

Function Calls

Function calls should include as many parameters as fit on each line, except where shorter lines are needed for clarity or documentation of the parameters. Continuation lines for function parameters may be indented to align with the opening parenthesis, or may have a four-space indent.

// GOOD:

CFArrayRef array = CFArrayCreate(kCFAllocatorDefault, objects, numberOfObjects,
                                 &kCFTypeArrayCallBacks);

NSString *string = NSLocalizedStringWithDefaultValue(@"FEET", @"DistanceTable",
    resourceBundle,  @"%@ feet", @"Distance for multiple feet");

UpdateTally(scores[x] * y + bases[x],  // Score heuristic.
            x, y, z);

TransformImage(image,
               x1, x2, x3,
               y1, y2, y3,
               z1, z2, z3);

Use local variables with descriptive names to shorten function calls and reduce nesting of calls.

// GOOD:

double scoreHeuristic = scores[x] * y + bases[x];
UpdateTally(scoreHeuristic, x, y, z);

Error Handling

When methods return an error parameter by reference, code MUST switch on the returned value and MUST NOT switch on the error variable.

// GOOD:

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

// AVOID:

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

Exceptions

Format exceptions with @catch and @finally labels on the same line as the preceding }. Add a space between the @ label and the opening brace ({), as well as between the @catch and the caught object declaration. If you must use Objective-C exceptions, format them as follows.

// GOOD:

@try {
    foo();
} @catch (NSException *ex) {
    bar(ex);
} @finally {
    baz();
}

Function Length

Prefer small and focused functions.

Long functions and methods are occasionally appropriate, so no hard limit is placed on function length. If a function exceeds about 40 lines, think about whether it can be broken up without harming the structure of the program.

Even if your long function works perfectly now, someone modifying it in a few months may add new behavior. This could result in bugs that are hard to find. Keeping your functions short and simple makes it easier for other people to read and modify your code.

When updating legacy code, consider also breaking long functions into smaller and more manageable pieces.

Vertical Whitespace

Use vertical whitespace sparingly. To allow more code to be easily viewed on a screen, avoid putting blank lines just inside the braces of functions. Limit blank lines to one or two between functions and between logical groups of code.

Naming

Names should be as descriptive as possible, within reason. Follow standard Objective-C naming rules.

Avoid non-standard abbreviations. Don’t worry about saving horizontal space as it is far more important to make your code immediately understandable by a new reader. For example:

// GOOD:

int numberOfErrors = 0;
int completedConnectionsCount = 0;
tickets = [[NSMutableArray alloc] init];
userInfo = [someObject object];
port = [network port];
NSDate *gAppLaunchDate;

// AVOID:

int w;
int nerr;
int nCompConns;
tix = [[NSMutableArray alloc] init];
obj = [someObject object];
p = [network port];

Any class, category, method, function, or variable name should use all capitals for acronyms and initialisms within the name. This follows Apple’s standard of using all capitals within a name for acronyms such as URL, ID, TIFF, and EXIF.

Names of C functions and typedefs should be capitalized and use camel case as appropriate for the surrounding code.

File Names

File names should reflect the name of the class implementation that they contain, including case.

Files containing code that may be shared across projects or used in a large project should have a clearly unique name, typically including the project or class prefix.

File names for categories should include the name of the class being extended, like GTMNSString+Utils.h or NSTextView+GTMAutocomplete.h

Class Names

Class names (along with category and protocol names) should start as uppercase and use mixed case to delimit words.

When designing code to be shared across multiple applications, prefixes are acceptable and recommended (e.g. GTMSendMessage). Prefixes are also recommended for classes of large applications that depend on external libraries.

Category Names

Category names should start with a prefix identifying the category as part of a project or open for general use.

The category name should incorporate the name of the class it’s extending. For example, if we want to create a category on NSString for parsing, we would put the category in a file named NSString+GTMParsing.h, and the category itself would be named GTMNSStringParsingAdditions. The file name and the category may not match, as this file could have many separate categories related to parsing. Methods in that category should share the prefix (gtm_MyCategoryMethodOnAString:) in order to prevent collisions in Objective-C’s global namespace.

// GOOD:

/** A category that adds parsing functionality to NSString. */
@interface NSString (GTMNSStringParsingAdditions)
- (NSString *)gtm_parsedString;
@end

Objective-C Method Names

Method and parameter names typically start as lowercase and then use mixed case.

Proper capitalization should be respected, including at the beginning of names.

// GOOD:

+ (NSURL *)URLWithString:(NSString *)URLString;

The method name should read like a sentence if possible, meaning you should choose parameter names that flow with the method name. Objective-C method names tend to be very long, but this has the benefit that a block of code can almost read like prose, thus rendering many implementation comments unnecessary.

Use prepositions and conjunctions like “with”, “from”, and “to” in the second and later parameter names only where necessary to clarify the meaning or behavior of the method.

// GOOD:

- (void)addTarget:(id)target action:(SEL)action;
- (CGPoint)convertPoint:(CGPoint)point fromView:(UIView *)view;
- (void)replaceCharactersInRange:(NSRange)aRange
            withAttributedString:(NSAttributedString *)attributedString;

A method that returns an object should have a name beginning with a noun identifying the object returned:

// GOOD:

- (Sandwich *)sandwich;

// AVOID:

- (Sandwich *)makeSandwich;

An accessor method should be named the same as the object it’s getting, but it should not be prefixed with the word get. For example:

// GOOD:

- (id)delegate;

// AVOID:

- (id)getDelegate;

Accessors that return the value of boolean adjectives have method names beginning with is, but property names for those methods omit the is.

// GOOD:

@property(nonatomic, getter=isGlorious) BOOL glorious;
- (BOOL)isGlorious;

BOOL isGood = object.glorious;
BOOL isGood = [object isGlorious];

// AVOID:

BOOL isGood = object.isGlorious;

Dot notation is used only with property names, not with method names.

// GOOD:

NSArray<Frog *> *frogs = [NSArray<Frog *> arrayWithObject:frog];
NSEnumerator *enumerator = [frogs reverseObjectEnumerator];

// AVOID:

NSEnumerator *enumerator = frogs.reverseObjectEnumerator;

These guidelines are for Objective-C methods only. C++ method names continue to follow the rules set in the C++ style guide.

Function Names

Regular functions have mixed case.

Ordinarily, functions should start with a capital letter and have a capital letter for each new word (a.k.a. “Camel Case” or “Pascal case”).

// GOOD:

static void AddTableEntry(NSString *tableEntry);
static BOOL DeleteFile(char *filename);

Because Objective-C does not provide namespacing, non-static functions should have a prefix that minimizes the chance of a name collision.

// GOOD:

extern NSTimeZone *GTMGetDefaultTimeZone();
extern NSString *GTMGetURLScheme(NSURL *URL);

Variable Names

Variable names typically start with a lowercase and use mixed case to delimit words.

Instance variables have leading underscores. File scope or global variables have a prefix g. For example: myLocalVariable, _myInstanceVariable, gMyGlobalVariable.

Common Variable Names

Readers should be able to infer the variable type from the name, but do not use Hungarian notation for syntactic attributes, such as the static type of a variable (int or pointer).

File scope or global variables (as opposed to constants) declared outside the scope of a method or function should be rare, and should have the prefix g.

// GOOD:

static int gGlobalCounter;

Instance Variables

Instance variable names are mixed case and should be prefixed with an underscore, like _usernameTextField.

Constants

Constant symbols (const global and static variables and constants created with #define) should use mixed case to delimit words.

Global and file scope constants should have an appropriate prefix.

// GOOD:

extern NSString *const GTLServiceErrorDomain;

typedef NS_ENUM(NSInteger, GTLServiceError) {
    GTLServiceErrorQueryResultMissing = -3000,
    GTLServiceErrorWaitTimedOut       = -3001,
};

Because Objective-C does not provide namespacing, constants with external linkage should have a prefix that minimizes the chance of a name collision, typically like ClassNameConstantName or ClassNameEnumName.

For interoperability with Swift code, enumerated values should have names that extend the typedef name:

// GOOD:

typedef NS_ENUM(NSInteger, DisplayTinge) {
    DisplayTingeGreen = 1,
    DisplayTingeBlue = 2,
};

Constants may use a lowercase k prefix when appropriate:

// GOOD:

static const int kFileCount = 12;
static NSString *const kUserKey = @"kUserKey";

Types and Declarations

Local Variables

Declare variables in the narrowest practical scopes, and close to their use. Initialize variables in their declarations.

// GOOD:

CLLocation *location = [self lastKnownLocation];
for (int meters = 1; meters < 10; meters++) {
  reportFrogsWithinRadius(location, meters);
}

Under Automatic Reference Counting, pointers to Objective-C objects are by default initialized to nil, so explicit initialization to nil is not required.

Unsigned Integers

Avoid unsigned integers except when matching types used by system interfaces.

Subtle errors crop up when doing math or counting down to zero using unsigned integers. Rely only on signed integers in math expressions except when matching NSUInteger in system interfaces.

// GOOD:

NSUInteger numberOfObjects = array.count;
for (NSInteger counter = numberOfObjects - 1; counter > 0; --counter)

// AVOID:

for (NSUInteger counter = numberOfObjects - 1; counter > 0; --counter)

Unsigned integers may be used for flags and bitmasks, though often NS_OPTIONS or NS_ENUM will be more appropriate.

Types with Inconsistent Sizes

Due to sizes that differ in 32- and 64-bit builds, avoid types long, NSInteger, NSUInteger, and CGFloat except when matching system interfaces.

Types long, NSInteger, NSUInteger, and CGFloat vary in size between 32- and 64-bit builds. Use of these types is appropriate when handling values exposed by system interfaces, but they should be avoided for most other computations.

// GOOD:

int32_t scalar1 = proto.intValue;
int64_t scalar2 = proto.longValue;
NSUInteger numberOfObjects = array.count;
CGFloat offset = view.bounds.origin.x;

// AVOID:

NSInteger scalar2 = proto.longValue;

File and buffer sizes often exceed 32-bit limits, so they should be declared using int64_t, not with long, NSInteger, or NSUInteger.

Comments

Comments are absolutely vital to keeping our code readable. The following rules describe what you should comment and where. But remember: while comments are important, the best code is self-documenting. Giving sensible names to types and variables is much better than using obscure names and then trying to explain them through comments.

Pay attention to punctuation, spelling, and grammar; it is easier to read well-written comments than badly written ones.

Comments should be as readable as narrative text, with proper capitalization and punctuation. In many cases, complete sentences are more readable than sentence fragments. Shorter comments, such as comments at the end of a line of code, can sometimes be less formal, but use a consistent style. When writing your comments, write for your audience: the next contributor who will need to understand your code. Be generous—the next one may be you!

File Comments

A file may optionally start with a description of its contents. Every file may contain the following items, in order:

License boilerplate if necessary. Choose the appropriate boilerplate for the license used by the project.
A basic description of the contents of the file if necessary.

If you make significant changes to a file with an author line, consider deleting the author line since revision history already provides a more detailed and accurate record of authorship.

Declaration Comments

Every non-trivial interface, public and private, should have an accompanying comment describing its purpose and how it fits into the larger picture.

Comments should be used to document classes, properties, ivars, functions, categories, protocol declarations, and enums.

// GOOD:

/**
 * A delegate for NSApplication to handle notifications about app
 * launch and shutdown. Owned by the main app controller.
 */
@interface MyAppDelegate : NSObject {
  /**
   * The background task in progress, if any. This is initialized
   * to the value UIBackgroundTaskInvalid.
   */
  UIBackgroundTaskIdentifier _backgroundTaskID;
}

/** The factory that creates and manages fetchers for the app. */
@property(nonatomic) GTMSessionFetcherService *fetcherService;

@end

Doxygen-style comments are encouraged for interfaces as they are parsed by Xcode to display formatted documentation. There is a wide variety of Doxygen commands; use them consistently within a project.

If you have already described an interface in detail in the comments at the top of your file, feel free to simply state, “See comment at top of file for a complete description”, but be sure to have some sort of comment.

Additionally, each method should have a comment explaining its function, arguments, return value, thread or queue assumptions, and any side effects. Documentation comments should be in the header for public methods, or immediately preceding the method for non-trivial private methods.

Use descriptive form (“Opens the file”) rather than imperative form (“Open the file”) for method and function comments. The comment describes the function; it does not tell the function what to do.

Document the thread usage assumptions the class, properties, or methods make, if any. If an instance of the class can be accessed by multiple threads, take extra care to document the rules and invariants surrounding multithreaded use.

Any sentinel values for properties and ivars, such as NULL or -1, should be documented in comments.

Declaration comments explain how a method or function is used. Comments explaining how a method or function is implemented should be with the implementation rather than with the declaration.

Implementation Comments

Provide comments explaining tricky, subtle, or complicated sections of code.

// GOOD:

// Set the property to nil before invoking the completion handler to
// avoid the risk of reentrancy leading to the callback being
// invoked again.
CompletionHandler handler = self.completionHandler;
self.completionHandler = nil;
handler();

When useful, also provide comments about implementation approaches that were considered or abandoned.

End-of-line comments should be separated from the code by at least 2 spaces. If you have several comments on subsequent lines, it can often be more readable to line them up.

// GOOD:

[self doSomethingWithALongName];  // Two spaces before the comment.
[self doSomethingShort];          // More spacing to align the comment.

Disambiguating Symbols

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

In Doxygen-style comments, prefer demarcating symbols with a monospace text command, such as @c.

Demarcation helps provide clarity when a symbol is a common word that might make the sentence read like it was poorly constructed. A common example is the symbol count:

// GOOD:

// Sometimes `count` will be less than zero.

or when quoting something which already contains quotes

// GOOD:

// Remember to call `StringWithoutSpaces("foo bar baz")`

Backticks or vertical bars are not needed when a symbol is self-apparent.

// GOOD:

// This class serves as a delegate to GTMDepthCharge.

Doxygen formatting is also suitable for identifying symbols.

// GOOD:

/** @param maximum The highest value for @c count. */

C Language Features

Macros

Avoid macros, especially where const variables, enums, XCode snippets, or C functions may be used instead.

Macros make the code you see different from the code the compiler sees. Modern C renders traditional uses of macros for constants and utility functions unnecessary. Macros should only be used when there is no other solution available.

Where a macro is needed, use a unique name to avoid the risk of a symbol collision in the compilation unit. If practical, keep the scope limited by #undefining the macro after its use.

Macro names should use SHOUTY_SNAKE_CASE – all uppercase letters with underscores between words. Function-like macros may use C function naming practices. Do not define macros that appear to be C or Objective-C keywords.

// GOOD:

#define GTM_EXPERIMENTAL_BUILD ...

// Assert unless X > Y
#define GTM_ASSERT_GT(X, Y) ...

// Assert unless X > Y
#define GTMAssertGreaterThan(X, Y) ...

// AVOID:

#define kIsExperimentalBuild ...

#define unless(X) if(!(X))

Avoid macros that expand to unbalanced C or Objective-C constructs. Avoid macros that introduce scope, or may obscure the capturing of values in blocks.

Avoid macros that generate class, property, or method definitions in headers to be used as public API. These only make the code hard to understand, and the language already has better ways of doing this.

Avoid macros that generate method implementations, or that generate declarations of variables that are later used outside of the macro. Macros shouldn’t make code hard to understand by hiding where and how a variable is declared.

// AVOID:

#define ARRAY_ADDER(CLASS) \
    -(void)add ## CLASS ## :(CLASS *)obj toArray:(NSMutableArray *)array

ARRAY_ADDER(NSString) {
    if (array.count > 5) {
        ...
    }
}

Examples of acceptable macro use include assertion and debug logging macros that are conditionally compiled based on build settings – often, these are not compiled into release builds.

Cocoa and Objective-C Features

Identify Designated Initializer

Clearly identify your designated initializer.

It is important for those who might be subclassing your class that the designated initializer be clearly identified. That way, they only need to override a single initializer (of potentially several) to guarantee the initializer of their subclass is called. It also helps those debugging your class in the future understand the flow of initialization code if they need to step through it. Identify the designated initializer using comments or the NS_DESIGNATED_INITIALIZER macro. If you use NS_DESIGNATED_INITIALIZER, mark unsupported initializers with NS_UNAVAILABLE.

Override Designated Initializer

When writing a subclass that requires an init... method, make sure you override the designated initializer of the superclass.

If you fail to override the designated initializer of the superclass, your initializer may not be called in all cases, leading to subtle and very difficult to find bugs.

Overridden NSObject Method Placement

Put overridden methods of NSObject at the top of an @implementation.

This commonly applies to (but is not limited to) the init..., copyWithZone:, and dealloc methods. The init... methods should be grouped together, followed by other typical NSObject methods such as description, isEqual:, and hash.

Convenience class factory methods for creating instances may precede the NSObject methods.

Initialization

Don’t initialize instance variables to 0 or nil in the init method; doing so is redundant.

All instance variables for a newly allocated object are initialized to 0 (except for isa), so don’t clutter up the init method by re-initializing variables to 0 or nil.

Use the following construction for initialization:

// GOOD:

- (instancetype)init {
    if (self = [super init]) {
        ...
    }
    return self;
}

Instance Variables In Headers Should Be `@protected` or `@private`

Instance variables should typically be declared in implementation files or auto-synthesized by properties. When ivars are declared in a header file, they should be marked @protected or @private.

// GOOD:

@interface MyClass: NSObject {
    @protected
    id _myInstanceVariable;
}
@end

Avoid `new`

Do not invoke the NSObject class method new, nor override it in a subclass. Instead, use alloc and init methods to instantiate retained objects.

Modern Objective-C code explicitly calls alloc and an init method to create and retain an object. As the new class method is rarely used, it makes reviewing code for correct memory management more difficult.

Keep the Public API Simple

Keep your class simple; avoid “kitchen-sink” APIs. If a method doesn’t need to be public, keep it out of the public interface.

Unlike C++, Objective-C doesn’t differentiate between public and private methods; any message may be sent to an object. As a result, avoid placing methods in the public API unless they are actually expected to be used by a consumer of the class. This helps reduce the likelihood they’ll be called when you’re not expecting it. This includes methods that are being overridden from the parent class.

Since internal methods are not really private, it’s easy to accidentally override a superclass’s “private” method, thus making a very difficult bug to squash. In general, private methods should have a fairly unique name that will prevent subclasses from unintentionally overriding them.

`#import` and `#include`

#import Objective-C and Objective-C++ headers, and #include C/C++ headers.

Choose between #import and #include based on the language of the header that you are including.

When including a header that uses Objective-C or Objective-C++, use #import. When including a standard C or C++ header, use #include. The header should provide its own #define guard.

Order of Includes

The standard order for header inclusion is the related header, operating system headers, language library headers, and finally groups of headers for other dependencies.

The related header precedes others to ensure it has no hidden dependencies. For implementation files the related header is the header file. For test files the related header is the header containing the tested interface.

A blank line may separate logically distinct groups of included headers.

Import headers using their path relative to the project’s source directory.

// GOOD:

#import "ProjectX/BazViewController.h"

#import <Foundation/Foundation.h>

#include <unistd.h>
#include <vector>

#include "base/basictypes.h"
#include "base/integral_types.h"
#include "util/math/mathutil.h"

#import "ProjectX/BazModel.h"
#import "Shared/Util/Foo.h"

Use Umbrella Headers for System Frameworks

Import umbrella headers for system frameworks and system libraries rather than include individual files.

While it may seem tempting to include individual system headers from a framework such as Cocoa or Foundation, in fact it’s less work on the compiler if you include the top-level root framework. The root framework is generally pre-compiled and can be loaded much more quickly. In addition, remember to use @import or #import rather than #include for Objective-C frameworks.

// GOOD:

@import UIKit;
#import <Foundation/Foundation.h>

// AVOID:

#import <Foundation/NSArray.h>
#import <Foundation/NSString.h>
...

Avoid Messaging the Current Object Within `init` and `dealloc`

Code in initializers and -dealloc should avoid invoking instance methods.

Superclass initialization completes before subclass initialization. Until all classes have had a chance to initialize their instance state any method invocation on self may lead to a subclass operating on uninitialized instance state.

A similar issue exists for -dealloc, where a method invocation may cause a class to operate on state that has been deallocated.

One case where this is less obvious is property accessors. These can be overridden just like any other selector. Whenever practical, directly assign to and release ivars in initializers and -dealloc, rather than rely on accessors.

// GOOD:

- (instancetype)init {
    if (self = [super init]) {
        _bar = 23;
    }
    return self;
}

Beware of factoring common initialization code into helper methods:

Methods can be overridden in subclasses, either deliberately, or accidentally due to naming collisions.
When editing a helper method, it may not be obvious that the code is being run from an initializer.

// AVOID:

- (instancetype)init {
    if (self = [super init]) {
        self.bar = 23;
        [self sharedMethod];
    }
    return self;
}

// GOOD:

- (void)dealloc {
    [_notifier removeObserver:self];
}

// AVOID:

- (void)dealloc {
    [self removeNotifications];
}

Setters copy NSStrings

Setters taking an NSString should always copy the string it accepts. This is often also appropriate for collections like NSArray and NSDictionary.

Never just retain the string, as it may be a NSMutableString. This avoids the caller changing it under you without your knowledge.

Code receiving and holding collection objects should also consider that the passed collection may be mutable, and thus the collection could be more safely held as a copy or mutable copy of the original.

// GOOD:

@property(nonatomic, copy) NSString *name;

- (void)setZigfoos:(NSArray<Zigfoo *> *)zigfoos {
    // Ensure that we're holding an immutable collection.
    _zigfoos = [zigfoos copy];
}

Use Lightweight Generics to Document Contained Types

All projects compiling on Xcode 7 or newer versions should make use of the Objective-C lightweight generics notation to type contained objects.

Every NSArray, NSDictionary, or NSSet reference should be declared using lightweight generics for improved type safety and to explicitly document usage.

// GOOD:

@property(nonatomic, copy) NSArray<Location *> *locations;
@property(nonatomic, copy, readonly) NSSet<NSString *> *identifiers;

NSMutableArray<MyLocation *> *mutableLocations = [otherObject.locations mutableCopy];

If the fully-annotated types become complex, consider using a typedef to preserve readability.

// GOOD:

typedef NSSet<NSDictionary<NSString *, NSDate *> *> TimeZoneMappingSet;
TimeZoneMappingSet *timeZoneMappings = [TimeZoneMappingSet setWithObjects:...];

Use the most descriptive common superclass or protocol available. In the most generic case when nothing else is known, declare the collection to be explicitly heterogenous using id.

// GOOD:

@property(nonatomic, copy) NSArray<id> *unknowns;

Avoid Throwing Exceptions

Don’t @throw Objective-C exceptions, but you should be prepared to catch them from third-party or OS calls. Use of @try, @catch, and @finally are allowed when required to properly use 3rd party code or libraries. If you do use them, please document exactly which methods you expect to throw.

`nil` Checks

Use nil checks for logic flow only.

Use nil pointer checks for logic flow of the application, not for preventing crashes when sending messages. Sending a message to nil reliably returns nil as a pointer, zero as an integer or floating-point value, structs initialized to 0, and _Complex values equal to {0, 0}.

Note that this applies to nil as a message target, not as a parameter value. Individual methods may or may not safely handle nil parameter values.

Note too that this is distinct from checking C/C++ pointers and block pointers against NULL, which the runtime does not handle and will cause your application to crash. You still need to make sure you do not dereference a NULL pointer.

BOOL Pitfalls

Be careful when converting general integral values to BOOL. Avoid comparing directly with YES.

BOOL in OS X and in 32-bit iOS builds is defined as a signed char, so it may have values other than YES (1) and NO (0). Do not cast or convert general integral values directly to BOOL.

Common mistakes include casting or converting an array’s size, a pointer value, or the result of a bitwise logic operation to a BOOL that could, depending on the value of the last byte of the integer value, still result in a NO value. When converting a general integral value to a BOOL use ternary operators to return a YES or NO value.

You can safely interchange and convert BOOL, _Bool and bool (see C++ Std 4.7.4, 4.12 and C99 Std 6.3.1.2). Use BOOL in Objective-C method signatures.

Using logical operators (&&, || and !) with BOOL is also valid and will return values that can be safely converted to BOOL without the need for a ternary operator.

// AVOID:

- (BOOL)isBold {
    return [self fontTraits] & NSFontBoldTrait;
}

- (BOOL)isValid {
    return [self stringValue];
}

// GOOD:

- (BOOL)isBold {
    return ([self fontTraits] & NSFontBoldTrait) ? YES : NO;
}

- (BOOL)isValid {
    return [self stringValue] != nil;
}

- (BOOL)isEnabled {
    return [self isValid] && [self isBold];
}

Also, don’t directly compare BOOL variables directly with YES. Not only is it harder to read for those well-versed in C, but the first point above demonstrates that return values may not always be what you expect.

// AVOID:

BOOL great = [foo isGreat];
if (great == YES) {
    // ...be great!
}

// GOOD:

BOOL great = [foo isGreat];
if (great) {
    // ...be great!
}

Interfaces Without Instance Variables

Omit the empty set of braces on interfaces that do not declare any instance variables.

// GOOD:

@interface MyClass : NSObject
// Does a lot of stuff.
- (void)fooBarBam;
@end

// AVOID:

@interface MyClass : NSObject {
}
// Does a lot of stuff.
- (void)fooBarBam;
@end

Cocoa Patterns

Delegate Pattern

Delegates, target objects, and block pointers should not be retained when doing so would create a retain cycle.

To avoid causing a retain cycle, a delegate or target pointer should be released as soon as it is clear there will no longer be a need to message the object.

If there is no clear time at which the delegate or target pointer is no longer needed, the pointer should only be retained weakly.

Block pointers cannot be retained weakly. To avoid causing retain cycles in the client code, block pointers should be used for callbacks only where they can be explicitly released after they have been called or once they are no longer needed. Otherwise, callbacks should be done via weak delegate or target pointers.

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 code in an Objective-C++ file outside of a class implementation, be consistent within the file.

// GOOD:

// file: cross_platform_header.h

class CrossPlatformAPI {
public:
    ...
    int DoSomethingPlatformSpecific();  // impl on each platform
private:
    int an_instance_var_;
};

// file: mac_implementation.mm
#include "cross_platform_header.h"

// A typical Objective-C class, using Objective-C naming.
@interface MyDelegate: NSObject {
@private
    int _instanceVar;
    CrossPlatformAPI *_backEndObject;
}

- (void)respondToSomething:(id)something;

@end

@implementation MyDelegate

- (void)respondToSomething:(id)something {
    // bridge from Cocoa through our C++ backend
    _instanceVar = _backEndObject->DoSomethingPlatformSpecific();
    NSString *tempString = [NSString stringWithFormat:@"%d", _instanceVar];
    NSLog(@"%@", tempString);
}

@end

// The platform-specific implementation of the C++ class, using
// C++ naming.
int CrossPlatformAPI::DoSomethingPlatformSpecific() {
    NSString *temp_string = [NSString stringWithFormat:@"%d", an_instance_var_];
    NSLog(@"%@", temp_string);
    return [temp_string intValue];
}

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