How to name a constant in Objective-C?

Question

What's the naming convention for constants in Objective-C (or most widely used way to name them)?

Is there a different criteria for extern constants?

Some styles I have seen:

NSString* const kPreferenceFirstRun = @"FirstRun";

// Replace "XY" by a prefix representing your company, project or module
NSString* const XYPreferenceFirstRun = @"FirstRun"; 

Answer 1

it's seems to me, the best practice is to name constants in upper-case. but cocoa-core developers don't seem to share my opinion)) they use CamelCase for constants

Answer 2

Personally, I tend to use the lowercase 'k' prefix because it's a little nicer on the eyes, and because it's clear that it's a constant (I never have any variable names that start with a 'k'). Also, Apple uses the 'k', so I just stuck with it.

I also tend to stay away from all-caps constants, because I've reserved all-caps for macro definitions. Just my two cents.

Answer 3

After a bit of googling I've found the official coding guidelines for Cocoa.

To sum up:

• Start with a two-letter prefix in ALL-CAPS
• Rest in UpperCamelCase
• Same criteria for extern constants

I agree with itaiferber that the k prefix style is clearer and also much more useful for autocompletion. It would be interesting to know if this style is more popular than the official guidelines.