From: Saynatkari <ruby-ml@...>
Date: 2005-04-04T06:56:18+09:00
Subject: Re: signleton_methods / methods / public_methods - weirdness?

David A. Black wrote:
> Hi --
> 
> On Mon, 4 Apr 2005, Johan Holmberg wrote:
> 
>>
>> Hi!
>>
>> I was trying to find out the "class methods" of some classes.
>> Looking in the PickAxe I found out that there are at least three 
>> methods that return almost the same thing for a class/module:
>>
>>    Object#singleton_methods(flag)
>>    Object#public_methods(flag)
>>    Object#methods(flag)
>>
>> So potentially we can get six (3 * 2) different results. To find out 
>> the difference between all invocations, I ran the methods on all 
>> builitin classes/modules, and compared the result. It turned out that 
>> I actually got 4 different results:
>>
>>    - methods(false) and singleton_methods(false)
>>      give the same result
>>
>>    - singleton_methods(true)
>>      gives a unique result
>>
>>    - public_methods(false)
>>      gives a unique result
>>
>>    - methods(true) and public_methods(true)
>>      give the same result
>>
>> The PickAxe said that Object#public_methods was a synonym for 
>> Object#methods. This is apparently not true (or true only when the 
>> argument is "true").
>>
>> To me it seem like these methods have "degenerated" into something 
>> that is almost impossible to explain. Neither the PickAxe nor the 
>> online-docs explains it in a way so I can understand the differences. 
>> Can anyone explain the logic behind these different methods and their 
>> results?
> 
> 
> I can offer one observation that might account for some of this:
> 
> "singleton_methods(true)" means "singleton methods on this object or,
> if the object is a Class, this object and its ancestral classes."  For
> example:
> 
>   irb(main):001:0> class A; def A.x; end; end; class B < A; end
>   => nil
>   irb(main):002:0> B.singleton_methods(false)
>   => []
>   irb(main):003:0> B.singleton_methods(true)
>   => ["x"]
> 
> I would argue that there is a bit of a contradiction here, arising
> from the special case of inheritance.  x is not really a singleton
> method of B; it's a singleton method of B's superclass, and the rules
> of inheritance allow the (arguably anomalous) behavior that the
> subclass can serve as the receiver for what would otherwise be a truly
> singleton method.
> 
> I believe this is the only scenario where, after doing this:
> 
>   def obj.meth; end
> 
> any object other than obj can call meth.  In other words, a Class's
> singleton methods ("class methods") don't quite behave in a singleton
> fashion.

other = obj.clone

> These true/false flags are awfully opaque, so
> B.singleton_methods(true) still sounds like it should be B's singleton
> methods, not those of B and other object(s).  Aside from the length of
> the method name, it should be something like:
> 
>   B.singleton_and_inherited_singleton_methods
> 
> to acknowledge that B is in the unusual position of being able to
> handle calls to the singleton methods of certain other objects.
> 
> Or -- B.class_methods.  I really like the fact that class methods in
> Ruby are just an application of the more general singleton-method
> principle.  But if they are in fact different at the language level,
> it might be best to label them.
> 
> 
> David

E