I think you are just confused by the overloaded use of the words objct and class as opposed to the ruby classes named Object and Class.
This diagram / project might help clarify http://objectgraph.rubyforge.org/dotOG.html From http://objectgraph.rubyforge.org/ Max On 5/16/11, John Merlino <li...@ruby-forum.com> wrote: > Hey all, > > I am a little confused about a tutorial I read. Here's an example below > taken from the tutorial: > > Object.instance_eval do > def has_attribute( *attrs ) > attrs.each do | attr | > self.class_eval %Q{ > def #{attr}=(val) > instance_variable_set("@#{attr}", val) > end > > def #{attr} > instance_variable_get("@#{attr}") > end > } > end > end > end > > class A > has_attribute :my_attribute, :another_attribute > end > > a = A.new > > puts a.methods - Object.methods > # => ["my_attribute", my_attribute=", "another_attribute", > "another_attribute="] > > a.my_attribute = 1 > a.my_attribute > # => 1 > > a.another_attribute = "A String" > a.another_attribute > # => "A String" > > THe guy says: > "The first instance_eval is used to add class method has_attribute into > Object so that we can call it in all the inherited class." > > I'm a little thrown off by this statement. First, Object itself is an > instance of class Class. Someone here even said before "Object is an > instance of Class". So "class Object end "implies that Object is an > instance of class, equivalent to: Object = Class.new. Hence, we can > invoke instance_eval on Object, since Object is an instance. What > confuses me here is has_attribute appears to be an instance method (e.g. > def a end) not class method (e.g. def self.a end). So why does guy say > we add class method has_attribute? > > In fact, the difference between Object class and Class class is that > when you add methods to class Class, those methods become available to > any class that is created as well (since all classes created using class > construct inherit from Class) and you can use those methods within any > class. However, that's not what we do above. We extend Object above. > When you instantiate a class, you inherently create an object instance, > so that object instance should have available the methods defined in > Object. So then how can we access that method within a class, such as > that being done in class A above? > > Thanks for response > > -- > Posted via http://www.ruby-forum.com/. > > -- > You received this message because you are subscribed to the Google Groups > "Ruby on Rails: Talk" group. > To post to this group, send email to rubyonrails-talk@googlegroups.com. > To unsubscribe from this group, send email to > rubyonrails-talk+unsubscr...@googlegroups.com. > For more options, visit this group at > http://groups.google.com/group/rubyonrails-talk?hl=en. > > -- You received this message because you are subscribed to the Google Groups "Ruby on Rails: Talk" group. To post to this group, send email to rubyonrails-talk@googlegroups.com. To unsubscribe from this group, send email to rubyonrails-talk+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/rubyonrails-talk?hl=en.
