Why does @YES give an "expected expression" error, but @(YES) compiles?

Question

Using XCode 4.4's Convert to Modern Objective C Syntax, my [NSNumber numberWithBool:YES] calls were converted to @(YES). I had some issue that I've now forgotten, and changed them myself to @YES, which is supposed to be the correct syntax.

However, doing so gives me the error:

Unexpected type name 'BOOL': expected expression

I know that there is an "expression" syntax but I don't see why I can't simply use @YES and @NO.

// Compiler error:
NSDictionary *userDefaultsDefaults = @{@"hasBeenLaunched": @YES};

// No error
NSDictionary *userDefaultsDefaults = @{@"hasBeenLaunched": @(YES)};

Why does @(YES) compile while @YES does not, and what I can do to remedy that?

Answer 1

Short answer:

Use @(YES) and @(NO)

---

Longer answer:

Have a look at this answer which explains that this is mostly appears to be an oversight on Apple's part.

A commenter on this answer also points out:

There is one small thing I'd like to warn about. Literal bools are also not supported because of this. However, a quick fix that I implemented was adding this to the beginning of one of my common headers (in an iOS project)

#ifndef __IPHONE_6_0 
#if __has_feature(objc_bool) 
#undef YES 
#undef NO 
#define YES __objc_yes 
#define NO __objc_no 
#endif 
#endif