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

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