Forum: Ruby what's different between self.method and class << self?

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Zhenning G. (Guest)
on 2008-10-21 11:24
we can define a instance method in lots way.
mostly, I saw people define like this:
1.
class A
  def self.class_method
  #some code here....
  end
end

2.
class A
  class << self
    def class_method
    #some code here....
    end
  end
end


==
the question confused me is what's the advantage of doing this in 2?
they'are different? which is your choose?
Patrick D. (Guest)
on 2008-10-21 16:22
(Received via mailing list)
On Tue, Oct 21, 2008 at 3:23 AM, Zhenning G.
<removed_email_address@domain.invalid>wrote:

> class A
> they'are different? which is your choose?
>
I asked this same question just a couple of weeks ago.  The answers I
was
given were:

Method 2:
1) Saves some typing
2) Has a slightly different mechanism for looking up class constants,
which
99.99% of the time won't be noticed.

Other than that there are no differences between methods 1 & 2.

--wpd
Zhenning G. (Guest)
on 2008-10-21 16:27
Patrick D. wrote:
> On Tue, Oct 21, 2008 at 3:23 AM, Zhenning G.
> <removed_email_address@domain.invalid>wrote:
>
>> class A
>> they'are different? which is your choose?
>>
> I asked this same question just a couple of weeks ago.  The answers I
> was
> given were:
>
> Method 2:
> 1) Saves some typing
> 2) Has a slightly different mechanism for looking up class constants,
> which
> 99.99% of the time won't be noticed.
>
> Other than that there are no differences between methods 1 & 2.
>
> --wpd

what's the meaning of saves some typing????
can you give me a example?
Patrick D. (Guest)
on 2008-10-21 16:33
(Received via mailing list)
>
> what's the meaning of saves some typing????
> can you give me a example?
> --
> Posted via http://www.ruby-forum.com/.
>
> Instead of having to type

def self.method
   blah
   blah
   blah
end

you can type (within the class << self clause)

def method
  blah
  blah
  blah
end

I didn't say it would save you a _lot_ of typing, just some :-)

--wpd
Shot (Piotr S.) (Guest)
on 2008-10-21 23:38
(Received via mailing list)
Zhenning G.:

> we can define a instance method in lots way.
> mostly, I saw people define like this:
> 1.
> class A
>   def self.class_method
>   #some code here....
>   end
> end

> 2.
> class A
>   class << self
>     def class_method
>     #some code here....
>     end
>   end
> end

> the question confused me is what's the advantage of doing this in 2?

You can work on the singleton’s properties with attr_* methods:

class Example
  class << self
    attr_accessor :prop
  end
end

(With the first approach you’d have to define self.prop and
self.prop= to be able to write code like Example.prop = 'value'.)

-- Shot
Shot (Piotr S.) (Guest)
on 2008-10-22 00:09
(Received via mailing list)
Shot (Piotr S.):

> (With the first approach you’d have to define self.prop and
> self.prop= to be able to write code like Example.prop = 'value'.)

…or use something like Rails’ cattr_* accessors – but they work on
class variables (as opposed to instance variables of the singleton.)

-- Shot
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