Multiple assignment in Perl

rnaeye has asked for the wisdom of the Perl Monks concerning the following question:

In Python I can do the following:

a, b = 0, 1
while b < 50:
    print(a, b)
    a, b = b, a + b
[download]

That is shorter version of the following assignment (I think they call it atomic version):

old_a = a
a = b
b = old_a + b
[download]

How do I do the first assignment in Perl? My Perl version is

 
use warnings;
use 5.18.2;

my ($a, $b) = (0, 1);
while ($b < 50) {
    say "$a $b";
    my $old_a = $a;
    $a = $b;
    $b = $old_a + $b;
}
[download]

Thank you.

Comment on Multiple assignment in Perl Select or Download Code

Replies are listed 'Best First'.
Re: Multiple assignment in Perl by Anonymous Monk on Jul 22, 2018 at 23:36 UTC
`($a, $b) = ($b, $a + $b);` [download]	[reply] [d/l]
Re^2: Multiple assignment in Perl by rnaeye (Friar) on Jul 23, 2018 at 00:23 UTC
That is embarrassing for me! It was the first thing I tried; it did not work for me at the time. I must have made a typo, etc. Thank you.	[reply]
Re^3: Multiple assignment in Perl by tobyink (Canon) on Jul 23, 2018 at 04:34 UTC
Maybe on your first attempt, you put an extra `my` in front of it? That would cause issues because it would declare two new variables within the `while` loop which would mask the old variables. Also, `$a` and `$b` are really bad variable names to choose in Perl. There are special variables with these names used by `sort` so using them for other stuff can occasionally cause issues. `$x` and `$y` would be fine, as would more meaningful variable names. toby döt ink	[reply] [d/l] [select]
Re^4: Multiple assignment in Perl by rnaeye (Friar) on Jul 24, 2018 at 13:05 UTC
Re: Multiple assignment in Perl by bart (Canon) on Jul 24, 2018 at 06:13 UTC
In Perl, the "`,`" operator has a lower precedence than "`=`". Therefore, your version means `$a, $b = $b, $a + $b` [download] which does, practically speaking, nothing. You have to add parens to enforce the proper precedence.	[reply] [d/l] [select]