From: 7stud -- <bbxx789_05ss@...>
Date: 2007-11-09T14:54:49+09:00
Subject: Re: 'Class.inherited' v. 'inherited' syntax inside Class

Thanks for the responses.

>David A. Black wrote:
> Hi --
> 
> On Fri, 9 Nov 2007, 7stud -- wrote:
> 
>>
>> Yet, in pickaxe2 on p. 445, the book lists inherited as a class method
>> of Class.
> 
> The term "class method" can refer to either of two things: an instance
> method of Class, or a singleton method of a given class. 
>

Wouldn't it be more proper to call an instance method of Class a "Class 
method" rather than a 'class method'.  In any case, I don't think your 
explanation applies to the page I referenced in pickaxe2.   Every class 
in the reference section starts with the class name a the beginning of a 
section, and then the methods for the class are listed on the subsequent 
pages.  But the methods are divided into the categories: Class methods, 
Instance methods, and Private methods.   On p. 445, it says:

class Class < Module
...
..


Class methods:
inherited
...

new
...

Instance methods:
allocate
...

new
..

superclass
...


Based on your explanation, I think that is a clear case for the errata. 
In fact, I checked ri, and ri produces this:


Class methods:
--------------
new


Instance methods:
-----------------
     allocate, inherited, initialize_copy, new, superclass
(END)


> When you call
> them, the technique is the same:
> 
>    class Class
>      def an_instance_method
>        puts "I'm an instance method of Class"
>      end
>    end
> 
>    class C
>      def C.a_singleton_method
>        puts "I'm a singleton method of C"
>      end
>    end
> 
>    C.an_instance_method
>    C.a_singleton_method
> 

Ok, thanks.  That explains why the inherit method in Class, when 
overridden in a user defined class, must be defined using the 'class 
method' syntax, e.g. UserClass.inherit.   I thought the method in Class 
was  named Class.inherit (because pickaxe2 said so), and in order to 
override that in a user defined class, you defined it with the same 
syntax, e.g. MyClass.inherit.



> So... when you do this:
> 
>    class Class
>      def inherited ...
> 
> you're defining an instance method called "inherited", and all
> instances of Class -- that is, all classes -- will have that method.
> 
> When you define Class.inherited, you're defining a singleton method on
> Class. The only thing that would be affected by that would be if you
> created a subclass of Class -- but Ruby doesn't permit that.
> 

Ok.  Thanks for clearing things up.
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