objective-c – ObjC类标识符和编译器魔术？

考虑：

@interface Foo : NSObject

+ (void) dump ;

@end

@implementation Foo

+ (Class) classOf1 {
    return self ;
}

+ (Class) classOf2 {
    return [Foo class] ;
}

+ (Class) classOf3 {
    return [[[Foo class] new] class] ;
}

+ (Class) classOf4 {
    return [[self new] class] ;
}

+ (Class) classOf5 {
    return [[[self alloc] init] class] ;
}

+ (Class) classOf6 {
    return [[[Foo alloc] init] class] ;
}

+ (Class) classOf7 {
    return [self class] ;
}

+ (void) dump {
    NSLog(@"classOf1 %@<0x%08.8lx>",[self classOf1],(unsigned long)[[self classOf1] hash]) ;
    NSLog(@"classOf2 %@<0x%08.8lx>",[self classOf2],(unsigned long)[[self classOf2] hash]) ;
    NSLog(@"classOf3 %@<0x%08.8lx>",[self classOf3],(unsigned long)[[self classOf3] hash]) ;
    NSLog(@"classOf4 %@<0x%08.8lx>",[self classOf4],(unsigned long)[[self classOf4] hash]) ;
    NSLog(@"classOf5 %@<0x%08.8lx>",[self classOf5],(unsigned long)[[self classOf5] hash]) ;
    NSLog(@"classOf6 %@<0x%08.8lx>",[self classOf6],(unsigned long)[[self classOf6] hash]) ;
    NSLog(@"classOf7 %@<0x%08.8lx>",[self classOf7],(unsigned long)[[self classOf7] hash]) ;
}

@end

并输出：

2013-07-04 03:20:20.404 WC[29862:c07] classOf1 Foo<0x0002a2e4>
    2013-07-04 03:20:21.075 WC[29862:c07] classOf2 Foo<0x0002a2e4>
    2013-07-04 03:20:21.628 WC[29862:c07] classOf3 Foo<0x0002a2e4>
    2013-07-04 03:20:22.229 WC[29862:c07] classOf4 Foo<0x0002a2e4>
    2013-07-04 03:20:22.805 WC[29862:c07] classOf5 Foo<0x0002a2e4>
    2013-07-04 03:20:23.387 WC[29862:c07] classOf6 Foo<0x0002a2e4>
    2013-07-04 03:20:25.235 WC[29862:c07] classOf7 Foo<0x0002a2e4>

所有7个案例都返回完全相同的值！

对我来说最令人费解的案例：

> classOf1和classOf7

在后者中,“自我”代表“Foo,这是一个阶级.那么班级的课程是什么？

> classOf5和classOf6

显然,“Foo”和“self”在这种情况下扮演着完全相同的角色.正如他们所做的那样

> classOf3和classOf4

在我看来,“Foo”是一个神奇的兔子.

您可以

@class Foo ;

在某种程度上

@class self ;

没有意义.

在词法分析器到运行时生成器流水线中,我可以理解比特流何时从一串字符变为标识符到语言相关的语义元素.但我很难弄清楚ObjC类标识符的确切性质.

任何人？

(这SO Question似乎无关)