From: Jeff Mitchell <quixoticsycophant@...>
Date: 2004-06-22T04:47:16+09:00
Subject: Re: About top-level method

--- Sam Sungshik Kong <ssk@chol.nospam.net> wrote:
> Hi, Lennon!
> 
> If I understand correctly, one can't call a private method via object name
> (receiver).
> Private methods can be called only with self.

You can also call a private method via send:

class A
   private
   def f
      99
   end
end

puts A.new.send(:f)
  # => 99

> 
> So the following code will cause an error (at the top level).
> 
> def foo #->this is a private instance method of Object
>   ...
> end
> 
> obj = Object.new
> 
> obj.foo #->Error, but in irb, it's ok.
> 
> Best explanation so far is that irb makes an exception for debugging
> purpose.
> 
> 
> While trying to find the answer, I met more confusing statements in the
> Programming Ruby (Classes and Objects chapter).
> 
> <snip>
> At the top level, we're executing code in the context of some predefined
> object. When we define methods, we're actually creating (private) singleton
> methods for this object. Instance variables belong to this object. And
> because we're in the context of Object, we can use all of Object's methods
> (including those mixed-in from Kernel) in function form. This explains why
> we can call Kernel methods such as puts at the top level (and indeed
> throughout Ruby): these methods are part of every object.
> </snip>
> 
> Is the above explanation correct?
> Do I create a singleton method if I define a method at the top level?

I would say the book explantion is not correct,

# courtesy dblack
module Kernel
   def singleton_class
      class << self
         self
      end
   end
end

def naked
   88
end

puts self.class == Object
   # => true
puts self.class.private_instance_methods.include?("naked")
   # => true
puts self.singleton_class.private_instance_methods.include?("naked")
   # => true

If the method was added only to the singleton class, as the book asserts, then
first "include?" check would give false.




		
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