You're just looking at it sideways. {grin}

The method needs to return an arrayref, which is then dereferenced by the @, and can thus be used in an lvalue context.

my $rec = bless {}; # main is the package
my @sideeffected = qw(a b c);
sub vals { return \@sideeffected }
@{$rec->vals()} = qw(d e f);
print "$_\n" for @sideeffected;
[download]

That prints d\ne\nf\n. Maybe you thought I was talking about the inner part? I was talking about the whole string of text from the "@" to the "}".