From: Rick DeNatale <rick.denatale@...>
Date: 2007-05-04T03:47:34+09:00
Subject: Re: Top-level

On 5/3/07, Lucas Holland <hollandlucas@gmail.com> wrote:
> Hello everyone!
>
> I'm currently diving a bit deeper into Ruby and I've already asked this
> question in the IRC (the folks there have been great I think I'm getting
> it 50%). The question's about top-level methods:
>
> Let's take puts as an example. Puts is inside of the Kernel module,
> which gets mixed into the Object class. So essentially, it's a private
> method of Object.

Yes

> When I call puts, I don't specify a receiver, so self
> is assumed (I think so).

 Yes

> In this case self refers to main, an instance
> of Object, automatically created.

Yes, well it's created when ruby starts up.

> So, I'm really calling main.puts. main
> is an instance of Object, so why is it able to call private methods of
> Object?

You're calling puts in the context of the top-level object.   In other
words self is the top-level object in code which is outside any class
or method definitions. The method puts is a private instance method,
so any Object can invoke it as long as the receiver is implicitly
'self':

irb(main):001:0> p self
main
=> nil
irb(main):002:0> puts "foo"
foo
=> nil
irb(main):003:0> self.puts "foo"
NoMethodError: private method `puts' called for main:Object
        from (irb):3

Note that the ruby enforces private methods is that you can't
explictily specify a receiver, even self.

Note that IRB treats methods defined at the top level a little
differently, in that they are public rather than private:

irb(main):004:0> def bar
irb(main):005:1>   puts "bar"
irb(main):006:1>   nil
irb(main):007:1>   end
=> nil
irb(main):008:0> bar
bar
=> nil
irb(main):009:0> self.bar
bar
=> nil

But
$ ruby -e'def bar;puts "bar";nil;end;bar;self.bar'
bar
-e:1: private method `bar' called for main:Object (NoMethodError)


> Help would be greatly appreciated!

HTH

-- 
Rick DeNatale

My blog on Ruby
http://talklikeaduck.denhaven2.com/