From: Stefan Lang <langstefan@...>
Date: 2005-09-24T20:47:03+09:00
Subject: Re: self.puts?

On Saturday 24 September 2005 12:30, Derek Chesterfield wrote:
> I am trying to convince myself that Ruby is fully OO [I'm not
> suggesting it isn't!].
>
> So writing 'object.method' sends a message 'method' to 'object',
> and writing 'method' implies sending to self. So how come the
> result of 'puts' is different to the result of 'self.puts'?
>
> > $ irb
> > irb(main):001:0> puts "hello"
> > hello
> > => nil
> > irb(main):002:0> self.puts "hello"
> > NoMethodError: private method `puts' called for main:Object
> >         from (irb):2
>
> I'm sure this is a semantic question, but I can't figure it out!
> How come 'self.puts' find the private puts method of Object,
> whereas 'puts' finds Kernel.puts?

Both find the private method "puts", which is defined in the
Kernel module. The Kernel module is included in the Object class.

Ruby doesn't allow that a private method is called with an explicit
receiver. If you write "self.puts", "self" is an explicit receiver.
If you simply write "puts" the receiver is implicitly "self".

Also try:

$irb
irb(main):001:0> class A
irb(main):002:1>   def foo
irb(main):003:2>     puts "hello, this is the foo method"
irb(main):004:2>     bar
irb(main):005:2>     self.bar
irb(main):006:2>   end
irb(main):007:1>   private
irb(main):008:1>   def bar
irb(main):009:2>     puts "hello, this is the bar method"
irb(main):010:2>   end
irb(main):011:1> end
=> nil
irb(main):012:0> a = A.new
=> #<A:0x402e30fc>
irb(main):013:0> a.bar
NoMethodError: private method `bar' called for #<A:0x402e30fc>
        from (irb):13
irb(main):014:0> a.foo
hello, this is the foo method
hello, this is the bar method
NoMethodError: private method `bar' called for #<A:0x402e30fc>
        from (irb):5:in `foo'
        from (irb):14


HTH,
  Stefan