return と return undef の違いを説明するときに使用したコード。list contextの場合に挙動が異なる

return-undef.t

use utf8;
use strict;
use warnings;
use Test::More;
use Test::Name::FromLine;

sub return_only  { return }
sub return_undef { return undef }

subtest 'scalar context' => sub {
    my $only  = return_only();
    is $only,  undef;

    my $undef = return_undef();
    is $undef, undef;
};

subtest 'list context' => sub {
    my @only  = return_only();
    is_deeply \@only,  [];

    my @undef = return_undef();
    is_deeply \@undef, [undef];
};

done_testing;