From: 7stud -- <bbxx789_05ss@...>
Date: 2009-05-03T05:24:49+09:00
Subject: Re: Help me understand 'self' vs current object

C. Dagnon wrote:
>
>Help me understand 'self' vs current object
>

class A
  def initialize
    @x = 10
  end

  def x=(val)
    @x = val
  end

  def x
    @x
  end

  def test1
    self.x = 0
  end
end

a = A.new
puts a.x

a.test1
puts a.x

--output:--
10
0

So far so good.


class A
  def meth
    puts "hello"
  end

  def test2
    meth
  end
end


a.test2

--output:--
hello

Bingo.  When ruby sees a method call without an object in front of it, 
the implied caller is self.  Inside the method test2, self is the object 
that called test2.  In this case, the object 'a' called test2, so inside 
test2 self=a.  The call to meth inside test2 has no object in front of 
it, so the implied caller is self. As a result, calling meth is 
equivalent to self.meth which is equivalent to a.meth.

Now consider this code:

class A
  def test3
    x = 0
  end
end

a.x = 10
a.test3
puts a.x

What's the output? Applying the previous lessons, 'a' is calling test3, 
so inside test3 self is 'a'.  The method call 'x=' inside test3 does not 
have an object in front of it, so the method call x= is equivalent to 
self.x=, which is equivalent to a.x=.  Here's the output:

--output:--
10

What the??!!  What happened?  As the smart guys pointed out in another 
current thread, when the ruby parser first encounters the line:

x = 10

it tags it with the message, "create a variable called x and assign 10 
to it".  As a result, ruby dutifully follows the parser's instructions 
rather than slapping 'self' in front of x=.  In other words, an 
unadorned name with = after it causes a local variable to be created 
rather than calling the 'name=' method.









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