Much of a muchness. length is a tiny bit quicker than eq, but otherwise I think they will act similarly.

Speed very much depends on what is the most likely value to occur in the tests. length for sure is not always faster. I prefer using defined-or:

$ cat test.pl
use 5.014;
use warnings;
use Benchmark qw(cmpthese);

foreach $a (undef, "", 0, 1, "x" x 60) {
    say "Testing for a = ", $a // "undef";

    cmpthese (-1, {
    def_eq  => sub { for (0..1000) { ! defined $a || $a eq ""   ? 1 : 
+0; }},
    def_len => sub { for (0..1000) { !(defined $a && length $a) ? 1 : 
+0; }},
    dor_eq  => sub { for (0..1000) { ($a // "") eq ""           ? 1 : 
+0; }},
    });
    }
$ perl test.pl
Testing for a = undef
           Rate  dor_eq  def_eq def_len
dor_eq   9135/s      --    -21%    -21%
def_eq  11499/s     26%      --     -1%
def_len 11605/s     27%      1%      --
Testing for a =
          Rate def_len  def_eq  dor_eq
def_len 7110/s      --     -8%    -25%
def_eq  7729/s      9%      --    -19%
dor_eq  9489/s     33%     23%      --
Testing for a = 0
           Rate def_len  def_eq  dor_eq
def_len  7518/s      --    -12%    -29%
def_eq   8533/s     14%      --    -19%
dor_eq  10577/s     41%     24%      --
Testing for a = 1
           Rate def_len  def_eq  dor_eq
def_len  7518/s      --    -12%    -29%
def_eq   8533/s     14%      --    -19%
dor_eq  10577/s     41%     24%      --
Testing for a = xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
+xxxxxx
           Rate def_len  def_eq  dor_eq
def_len  7450/s      --    -13%    -30%
def_eq   8533/s     15%      --    -20%
dor_eq  10676/s     43%     25%      --
$
[download]


Enjoy, Have FUN! H.Merijn

Speed very much depends on what is the most likely value to occur in the tests. length for sure is not always faster.

Hm. You seem to be implying that the speed of length varies with the length of the string?

Whilst that would make sense with C; it makes no sense at all with length, which doesn't need to scan the string to find its length.

Which makes me a little suspicious of the benchmark.

Update: Of course; the affect you are seeing it due to stringification of numeric values.

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