how to control self.method access

rubyonrails-talk
1

i think self.method just like class method,so if i want to define it as a private method,i should use

private_class_method :my_method

but i found follow code in < <Agile Web Development with Rails>>

private def self.hash_password(password)   Digest::SHA1.hexdigest(password) end

just a mistake or there have some thing which i cannot get?

2

I've never used private_class_method but based on the Ruby API it should do what you want. The agile example will work too, and is probably a bit more convenient if you have more than one private method because the private declaration applies to everything that comes after it.

I always group my class methods in a "class << self" block and then put private class methods at the end of that block like this:

class Foo   class << self     def some_public_class_method       ....     end

    private     def some_private_class_method       ...     end   end end

Aaron

3

but I test follow code

4

I ran your test code and was surprised to see that the private declaration didn't apply to the class method. I guess private only applies to instance methods. So that leaves "private_class_method" and a "class << self" block as the two ways to make class methods private.

Aaron

5

so, the demo code in <<agile>> was wrong? I hava another question,If i keep class methods private via private_class_method method,I can not invoke these methods see this

6

--------------------------- class Test

  def say     Test::say_hello   end

  def self.say_hello     p 'Hello'   end

  private_class_method :say_hello end

Test.new.say ---------------------- run above code will get follow error message Test.rb:4:in `say': private method `say_hello' called for Test:Class (NoMethodError) How should I do can both make class methods are private and can be invoked

You can't access the private class method from an object instance because they are in different classes. Every ruby object has what is called a singleton class that contains per-object attributes. See Chapter 24 "Classes and Objects" in the Pickaxe book for a much more thorough explanation.

I took your example above and modified it slightly to show you one possible way to make it work:

class Test   class << self     def say_hello_accessor       say_hello     end

    private     def say_hello       p 'Hello'     end   end

  def say     self.class.say_hello_accessor   end end

Test.new.say

Hope this helps.

Aaron

7

Thanks Aaron! It works.But I feel this way put some additional complexity into Test class. if there have any way can define a private class method and invoke it directly, that would be nice! you said:'You can't access the private class method from an object instance,because they are in different classes'.you mean every instance have an own class and each of them are different,that's the reason I can not invoke private class method in instance method,am i right?