Rails - Jan 2006 - Question about self and private

Hi!

There''s something I don''t understand yet about static/private
methods. I
hope someone can explain...

E.g.:

class SayHello
   def hello(who)
     puts "Hello, " + who + "!"
   end
   def self.say(words)
     puts words
   end
end

hello = SayHello.new
hello.hello "World"	: Hello World!
hello.say "hi"		: Error
SayHello.say "hi"	: hi

OK, this is clear to me, but now...

class SayHello
   private
   def hello(who)
     puts "Hello, " + who + "!"
   end
   def self.say(words)
     puts words
   end
end

Both methods are private now.

hello = SayHello.new
hello.hello "World"	: Error because the method is private
hello.say "hi"		: Error because the method is static
SayHello.say "hi"	: hi

The last one I don''t understand. How come it returns "hi"
eventhough
it''s a private method? Can someone shed some light?

Thanks,
Mischa.

Mischa Berger wrote:
> class SayHello
>   private
>   def hello(who)
>     puts "Hello, " + who + "!"
>   end
>   def self.say(words)
>     puts words
>   end
> end
> 
> Both methods are private now.
Nope private, protected and public modifiers have only effect on instance
methods (that have an implicit "self" as receiver). If you want to
define
a private class method you need to make available that implicit
"self":

class SayHello
  private
  def hello(who)
    puts "Hello, " + who + "!"
  end
  class << self
    private
    def say(words)
      puts words
    end
  end
end

Now both methods are private. You can only call them on self, this means
that SayHello.say is only callable by another class method.

zsombor
-- 
Company  - http://primalgrasp.com
Thoughts - http://deezsombor.blogspot.com

On Tue, 2006-01-17 at 11:29 +0200, Dee Zsombor wrote:
> class SayHello
>   private
>   def hello(who)
>     puts "Hello, " + who + "!"
>   end
>   class << self
>     private
>     def say(words)
>       puts words
>     end
>   end
> end
> 
You can''t do this though:

class SayHello
  self.private
  def self.say(words)
    puts words
  end
end

as "private" is itself a private method :)

NoMethodError: private method `private'' called for SayHello:Class

Dee Zsombor wrote:
> Mischa Berger wrote:
> 
>>class SayHello
>>  private
>>  def hello(who)
>>    puts "Hello, " + who + "!"
>>  end
>>  def self.say(words)
>>    puts words
>>  end
>>end
>>
>>Both methods are private now.
> 
> 
> Nope private, protected and public modifiers have only effect on instance
> methods (that have an implicit "self" as receiver). If you want
to define
> a private class method you need to make available that implicit
"self":
Well, actually I was asking cause I saw a code sample in the "Agile Web 
Development with Rails" book (pp. 510: private def self.hash_password) 
that didn''t make sense to me. I don''t mind my methods not
being private,
so I guess I''ll just leave out "private". Thanks for clearing
things up.

Mischa.

>>> class SayHello
>>>  private
>>>  def hello(who)
>>>    puts "Hello, " + who + "!"
>>>  end
>>>  def self.say(words)
>>>    puts words
>>>  end
>>> end
An even simpler way is to use ''private_class_method''

class SayHello
  def self.say(words)
    puts words
  end
  private_class_method :say
end

Zsombor

-- 
Company  - http://primalgrasp.com
Thoughts - http://deezsombor.blogspot.com