Hello LanX,

Thanks for that, it’s good to know. Perl continues to surprise! I looked in the Camel Book, but the section on “List Assignment”¹ doesn’t cover this behaviour. Do you know where it’s documented?

I’m intrigued to know how Perl accomplishes this. I wrote the following, but it left me none the wiser:

#! perl
use strict;
use warnings;
use feature qw(say state);

#say 'f = ', f(), ', g = ', g();

( f(), g() ) = ( g(), f() );

#say 'f = ', f(), ', g = ', g();

sub f : lvalue
{
    state  $f = 'first';
    say 'f(', $f, ')';
    return $f;
}

sub g : lvalue
{
    state  $g = 'second';
    say 'g(', $g, ')';
    return $g;
}
[download]

12:58 >perl 1193_SoPW.pl
g(second)
f(first)
f(first)
g(second)

12:58 >
[download]

It looks as though the virtual machine:

1. accesses the right-hand variables
2. accesses the left-hand variables
3. performs the assignments

So it must create temporary copies of the right-hand variables “under the hood”?

¹Chapter 2, pages 82–83 in the 4^th Edition.