How to name a constant in Objective-C?

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

Is there a different criteria for e开发者_高级运维xtern 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"; 

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

To sum up:

• Start with a two- or three-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.

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