use constant DEBUG => 0;

##</code><code>##

use strict;
use warnings;
use constant DEBUG => 0;

print "Hello World\n";
print "This is a debug Statement\n" if DEBUG;
print "Goodbye Cruel Word\n";

##</code><code>##

use constant ('DEBUG', 0);
use warnings;
use strict 'refs';
print "Hello World\n";
'???';
print "Goodbye Cruel Word\n";

##</code><code>##

use strict;
use warnings;
use Benchmark qw( cmpthese );
use constant DEBUG => 0;

my $b = 100;
cmpthese -10, {
    constant   => sub { my $a = 10 * $b; $a = 10 * $b if DEBUG; },
    noconstant => sub { my $a = 10 * $b; },
};


##</code><code>##

                Rate   constant noconstant
constant   1498536/s         --       -17%
noconstant 1796946/s        20%         --