Best way to define Constants in Objective-C

Question

I am defining constants with proper naming convention in objective-C but after having some search on internet, I found three different naming conventions for defining the constants. Those of given below.

NSString *const kModel_userID;
NSString *const k_model_user_id;
NSString *const kUserId;

Please check these and help me out which is the best way convention for constants in objective-C. Please give me valid reason if you like any convention. Also If you have any other convention please share that too. Thanks

Answer 1

Prefix + Scope/Class + Identifier/Detail + Suffix/ConstantType.

Omit what does not apply.

Example:

// A NSNotification name, pertaining to NSApplication
NSApplicationWillBecomeActiveNotification
PrClass      Identifier      SuffxType

Pretty idiomatic and easy to grok, IMO ;)

You use a similar form with enums:

// enum NSApplicationDelegateReply
NSApplicationDelegateReplySuccess
PrClass      Enum         Identifier

I should also note that you should choose prefixes for your APIs which have 3 or more characters, to reduce the likelihood of colliding with Apple's or others' APIs.

The k prefix is an older convention. You will find it in many of the C APIs on OS X and iOS, such as the Core* frameworks. It's not very idiomatic for Objective-C APIs these days. It's used in some third party projects, but the uppercase prefix convention is most recognizable for Objective-C. Even the k prefixed constants use identifiers to 'namespace' their APIs, e.g. kCTLineTruncationStart. Smart.