# Compiles each pattern once since m// realises
# you're using the same pattern twice in a row.
for my $re (qw( foo bar )) {
   for (1..2) {
      /$re/
   }
}

##</code><code>##

# Compiles each pattern twice
for (1..2) {
   for my $re (qw( foo bar )) {
      /$re/
   }
}

##</code><code>##

# Compiles each pattern once
my @res = map qr/$_/, qw( foo bar );
for (1..2) {
   for my $re (@res) {
      /$re/
   }
}

##</code><code>##

# Doesn't recompile $re if it's a qr//.
/$re/

# Stringifies and recompiles $re if it's a qr//,
# but it should be subject to the caching mentioned above.
/x$re/