可以添加“键控下标”到类对象？ [英] Is it possible to add "keyed-subscripting" to Class objects?

问题描述

在...的静脉中...

In the vein of...

@implementation MyClass
- (id) objectForKeyedSubscript:(id)k { 
       return [self something:k]; 
}

也可以下标 / code> objects？我也是，我想知道，与你..但认为我会发布这个问题，因为我测试了，自己...

Is it also possible to "subscript" Class objects? I too, am about to find out, with you.. but thought I would post this question as I tested it out, myself...

+ (id) objectForKeyedSubscript:(id)k { 
       return [self.shared something:k]; 
}

和唉...不是...

And alas.. it is not...

id x = MyClass[@"document"];

错误：意外接口名称'MyClass'：预期表达式

error: unexpected interface name 'MyClass': expected expression

但是为什么，Daddy？ $ c>'如果你问我，请务必得到 NSObject 的短端。

But why, Daddy? Class' sure get the short end of NSObject's stick, if you ask me.

推荐答案

Josh Caswell的评论指出了问题：

类型名称。尝试一个类对象在一个变量。 id myClass = [MyClass class]; myClass [@document]; 或 [MyClass class] [@document]

You're using the type name. Try it with a class object in a variable. id myClass = [MyClass class]; myClass[@"document"]; Or [MyClass class][@"document"]

我尝试过的SWEAR。 BIBLE 。但是证明是在布丁...

I SWEAR I had tried that. BIBLE. But the proof is in the pudding...

@interface MyClass : NSObject
@property (readonly) id  boring;
@end
@implementation MyClass
- boring   { return @"typical"; }
+ document { return  @"YEEHAW"; }
- objectForKeyedSubscript:key { return [self valueForKey:key]; }
+ objectForKeyedSubscript:key { 
  return [self performSelector:NSSelectorFromString(key)]; 
}
@end

...

id a = MyClass.new;
id x = a[@"boring"];   // "typical" (via "normal" keyed subscription)
id b = MyClass.class;
   x = z[@"document"]; // "YEEHAW" (via CLASS keyed-subscript!)

-liner freaky-deaky's 在那里...

or for all my one-liner freaky-deaky's out there...

x = ((id)MyClass.class)[@"document"] // "YEEHAW" 

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