$n = 10_000_000;
print ": ";  <>;                                       # 2MB
$f = 1;
for (0..$n-1) { if ($f) { $f = 0; print ": "; <>; } }  # 2MB

##</code><code>##

$n = 10_000_000;
print ": "; <>;                                   #   2MB
push @a, --$n while $n;
print ": ";  <>;                                  # 240MB
$f = 1;
for (@a) { if ($f) { $f = 0; print ": "; <>; } }  # 240MB

##</code><code>##

$n = 10_000_000;
print ": ";  <>;                                         #   2MB
$f = 1;
grep { if ($f) { $f = 0; print ": "; <>; } 0 } 0..$n-1;  # 240MB  <--

##</code><code>##

$n = 10_000_000;
print ": "; <>;                                     #   2MB
push @a, --$n while $n;
print ": "; <>;                                     # 240MB
$f = 1;
grep { if ($f) { $f = 0; print ": "; <>; } 0 } @a;  # 280MB  <--