That's because the (scalar) operator of an op= imposes scalar context on the lists and so only the last element of each list is affected:
c:\@Work\Perl\monks>perl -wMstrict -le
"my ($x, $y, $z) = (30, 40, 50);
($x, $y, $z) += (3, 4, 5);
print qq{$x, $y, $z};
"
Useless use of a constant in void context at -e line 1.
Useless use of a constant in void context at -e line 1.
Useless use of private variable in void context at -e line 1.
Useless use of private variable in void context at -e line 1.
30, 40, 55
Raku can do these kinds of list operations; see Raku Programming/Meta Operators.
Update: I'm not aware that you can do this with pure lists in Perl 5, but it can certainly be done with arrays:
c:\@Work\Perl\monks>perl -wMstrict -le
"my @ra = (30, 40, 50);
my @rb = ( 3, 4, 5);
;;
$ra[$_] += $rb[$_] for 0 .. $#ra;
print qq{@ra};
"
33 44 55
And via List::MoreUtils::pairwise():
c:\@Work\Perl\monks>perl -wMstrict -le
"use List::MoreUtils qw(pairwise);
use vars qw($a $b);
;;
my @ra = (30, 40, 50);
my @rb = ( 3, 4, 5);
;;
my @rc = pairwise { $a + $b } @ra, @rb;
print qq{@rc};
"
33 44 55
or
c:\@Work\Perl\monks>perl -wMstrict -le
"use List::MoreUtils qw(pairwise);
use vars qw($a $b);
;;
my @ra = (30, 40, 50);
my @rb = ( 3, 4, 5);
;;
pairwise { $a += $b } @ra, @rb;
print qq{@ra};
"
33 44 55
(The use vars qw($a $b); statement quiets some warnings.)
Give a man a fish: <%-{-{-{-<
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