From: Josh Cheek <josh.cheek@...>
Date: 2011-10-05T21:59:03+09:00
Subject: Re: Local vs method vs instance

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On Wed, Oct 5, 2011 at 4:00 AM, Brian Candler <b.candler@pobox.com> wrote:

> Darryl Pierce wrote in post #1025016:
> > On 10/04/2011 11:42 AM, Chris Hulan wrote:
> >> but doing it this way makes the x public readable, so should only be
> >> used if that is needed
> >> I'd stick with using @x
> >
> > AH! That's what I missing, and what he meant by "the method". Okay. The
> > OP though didn't have the attr_accessor on the fields, though, that I
> > remember.
>
> This was implied by the use of 'other.x'. If you can write 'other.x'
> then that object must have a method called 'x'. Since we're talking
> about adding two objects of the same class, this means self also has a
> method 'x', and you can call this just using 'x'.
>
> Now, if you don't want to have accessors on your Point class, then it
> gets a little bit messy to tinker with the internals of the other
> object: e.g.
>
>  @x + other.instance_variable_get(:@x)
>
> or
>
>  @x + other.instance_eval { @x }
>
> I think you could also use a 'protected' accessor method, but I've never
> found the need to use those.
>
> --
> Posted via http://www.ruby-forum.com/.
>
>
For that, you could use protected:


class UselessPoint
  def initialize(x, y)
    @x, @y = x, y
  end

  def +(point)
    UselessPoint.new point.x+x, point.y+y
  end

protected

  attr_reader :x, :y
end

p1 = UselessPoint.new 1, 2
p2 = UselessPoint.new 3, 4

p1 + p2 # => #<UselessPoint:0x007fdc6208b970 @x=4, @y=6>
p1.x # =>
# ~> -:19:in `<main>': protected method `x' called for
#<UselessPoint:0x007fdc6208ba10 @x=1, @y=2> (NoMethodError)

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