From: dblack@...
Date: 2007-01-27T20:46:47+09:00
Subject: Re: pass by reference?

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Hi --

On Sat, 27 Jan 2007, Wolfgang N=E1dasi-Donner wrote:

>>>>>> Code >>>>>
>
> def modifying(a_param)
>  a_param =3D "hi"
> end
>
> def modifying2(a_param=3Da_value)
>  a_param =3D "hi"
> end
>
> def modifying3(a_param)
>  a_param[0..-1]=3D "hi"
> end
>
> a_value =3D "low"
> modifying a_value
> case a_value
> when "hi"
>  puts "Passed by reference"
> when "low"
> puts "Passed by value"
> else
> puts "Passed away"
> end
>
> a_value =3D "low"
> modifying2 a_value
> case a_value
> when "hi"
>  puts "Passed by reference"
> when "low"
> puts "Passed by value"
> else
> puts "Passed away"
> end
>
> a_value =3D "low"
> modifying3 a_value
> case a_value
> when "hi"
>  puts "Passed by reference"
> when "low"
> puts "Passed by value"
> else
> puts "Passed away"
> end
>
>>>>>> Output >>>>>
>
> Passed by value
> Passed by value

But you've broken the bindings.  It's a whole new ballgame, as we say
here :-)

> Passed by reference

I would say: a reference, passed by value.

>>>>>> EoE >>>>>
>
> I would name it somehow "call by assignment of value to local variable",=
=20
> because the value of the actual parameter is assigned to the local variab=
le=20
> used as a formal parameter.
>
> except for "Fixnum" etc. this is a pointer to an object. I one changes th=
e=20
> object itself, it will work like  "by reference", otherwise only the loca=
l=20
> variable is affected, without having any effect to the outside world.

I consider the variable assignment semantics to be a separate matter.
For example:

   def x(a)
     a =3D "hello"
   end

Here, Ruby's rule is that the second a is a completely new binding,
and destroys the original binding.  I don't think that has anything to
do with whether the first a is a reference or a value.  In other
words, even if Ruby had pass by reference, I assume that a =3D "hello"
would still destroy the binding and create a new local variable.

(Of course, it's purely speculative, since it would be a completely
different language.)


David

--=20
Q. What is THE Ruby book for Rails developers?
A. RUBY FOR RAILS by David A. Black (http://www.manning.com/black)
    (See what readers are saying!  http://www.rubypal.com/r4rrevs.pdf)
Q. Where can I get Ruby/Rails on-site training, consulting, coaching?
A. Ruby Power and Light, LLC (http://www.rubypal.com)
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