From: Xavier Noria <fxn@...>
Date: 2007-01-28T04:41:03+09:00
Subject: Re: pass by reference?

On Jan 27, 2007, at 8:25 PM, Thomas Hafner wrote:

> That's another story. With the code above you rather reset b to a new
> object instead of modifying the passed object. Look here:
>
> def m(b)
>   b.shift
>   b.unshift(7)
> end
> a = [3]
> m(a)
> => [7]
>
> Would that be the same with pass-by-value? No, I don't think so.

Yes, that's the usual point in the discussion. Being able to change  
the internal state of mutable objects is not a test for pass-by- 
reference. Java is pass-by-value for instance (according to the JLS)  
and that test passes.

Problem with the assignment-seen-in-the-caller test is what dblack  
pointed out, it mixes assigment semantics.

In Perl, which is pass by reference, you can do this for example:

   $ perl -wle '$x = 0; sub { ++$_[0] }->($x); print $x'
   1

-- fxn