Ooooh... fun question. The answer is a c-ism.
@interface MyClass : NSObject
Now, say you have:
MyClass *m = nil;
In that context, the compiler sees
MyClass as a type definition. The
* says that the variable
m is a
pointer to a hunk o' memory that contains one (or many -- don't forget your C pointer-fu) MyClass instances.
In other words,
MyClass is a type.
But, in the context of something like:
[someInstance isKindOfClass: x ];
x must be an rvalue or, in human terms, the value of an expression. A type, however, cannot be used as an rvalue.
[MyClass class] works is actually a bit of a hack, both in the language and the compiler in that the grammar specifically allows a type name to be the message receiver (to be the target of a method call).
And, as a matter of fact, you can do:
typedef MyClass Foo;
It'll all work. However, you can't do the following but the error message is illuminating:
error: ‘NSUInteger’ is not an Objective-C class name or alias
Now, why not special case it everywhere as a bare name?
That colludes type names and rvalues and you quickly end up having to swallow something like
[foo isKindOfClass: (MyClass)]; while barfing on
[foo isKindOfClass: (MyClass *)]; which then encroaches upon typecasting territory in a rather uncomfortable fashion.