sub foo
{
    .....

    return @foo;
}

my $num_foo = foo( @args );

##</code><code>##

my @x = 1 .. 1_000_000;
sub want { return wantarray ? @x : $#x + 1; }
sub nowant { return @x; }

cmpthese( -10, {
    '1nowant' => sub { my $x = nowant(); },
    '2want'   => sub { my $x = want(); },
    '3nowant_list' => sub { my $x = () = nowant(); },
    '4want_list'   => sub { my $x = () = want(); },
});
--------
Benchmark: running 1nowant, 2want, 3nowant_list, 4want_list for at least 10 CPU seconds...
   1nowant: 10 wallclock secs (10.25 usr +  0.00 sys = 10.25 CPU) @ 582570.73/s (n=5971350)
     2want: 10 wallclock secs (10.05 usr +  0.00 sys = 10.05 CPU) @ 578237.81/s (n=5811290)
3nowant_list: 11 wallclock secs (10.84 usr +  0.00 sys = 10.84 CPU) @  1.11/s (n=12)
4want_list: 11 wallclock secs (10.66 usr +  0.00 sys = 10.66 CPU) @  1.13/s (n=12)
                 Rate 3nowant_list   4want_list        2want      1nowant
3nowant_list   1.11/s           --          -2%        -100%        -100%
4want_list     1.13/s           2%           --        -100%        -100%
2want        578238/s    52234049%    51366692%           --          -1%
1nowant      582571/s    52625456%    51751600%           1%           --

##</code><code>##

Benchmark: running 1nowant, 2want, 3nowant_list, 4want_list for at least 10 CPU seconds...
   1nowant: 13 wallclock secs (10.67 usr +  0.00 sys = 10.67 CPU) @ 558715.46/s (n=5961494)
     2want: 12 wallclock secs (10.66 usr +  0.00 sys = 10.66 CPU) @ 390887.71/s (n=4166863)
3nowant_list: 11 wallclock secs (10.75 usr +  0.00 sys = 10.75 CPU) @  1.12/s (n=12)
4want_list: 11 wallclock secs (10.72 usr +  0.00 sys = 10.72 CPU) @  1.12/s (n=12)
                 Rate 3nowant_list   4want_list        2want      1nowant
3nowant_list   1.12/s           --          -0%        -100%        -100%
4want_list     1.12/s           0%           --        -100%        -100%
2want        390888/s    35016924%    34919202%           --         -30%
1nowant      558715/s    50051494%    49911815%          43%           --