p5pRT
commented
19 years ago From @abigail
Created by @abigail
I would expect
grep {EXPR} LIST
to be somewhat slower than
grep EXPR\, LIST
For instance\, the following benchmark shows the block version to be 5% slower:
use Benchmark qw /cmpthese/;
our @array = 101 .. 200;
cmpthese -2 => { grep_eq_expr => '$::a1 = grep $_ == 50\, @::array'\, grep_eq_blck => '$::a2 = grep {$_ == 50} @::array'\, };
__END__ Rate grep_eq_blck grep_eq_expr grep_eq_blck 28902/s -- -5% grep_eq_expr 30282/s 5% --
If\, however\, the expression is a regexp\, things change drastically:
use Benchmark qw /cmpthese/;
our @array = 101 .. 200;
cmpthese -2 => { grep_re_expr => '$::b1 = grep /^50$/\, @::array'\, grep_re_blck => '$::b2 = grep {/^50$/} @::array'\, };
__END__ Rate grep_re_blck grep_re_expr grep_re_blck 6455/s -- -69% grep_re_expr 20848/s 223% --
This difference in speed surprises me.
It's not the fact that it's a regexp that's run inside a block\, as a similar for loop doesn't show the huge difference:
use Benchmark qw /cmpthese/;
our @array = 101 .. 200;
cmpthese -2 => {
for_eq_expr => '$::c1 = 0; $_ == 50 and $::c1 ++ for @::array'\,
for_eq_blck => '$::c2 = 0; for (@::array) {$_ == 50 and $::c2 ++}'\,
};
__END__ Rate for_eq_blck for_eq_expr for_eq_blck 23640/s -- -5% for_eq_expr 24992/s 6% --
use Benchmark qw /cmpthese/;
our @array = 101 .. 200;
cmpthese -2 => {
for_re_expr => '$::d1 = 0; /^50$/ and $::d1 ++ for @::array'\,
for_re_blck => '$::d2 = 0; for (@::array) {/^50$/ and $::d2 ++}'\,
};
__END__ Rate for_re_blck for_re_expr for_re_blck 19091/s -- -2% for_re_expr 19545/s 2% --
In both cases\, the block version is slower\, but by a small margin.
So\, I suspect a bug somewhere.
I'll be leaving for my honeymoon and YAPC::AU tomorrow morning\, so it might be a while before I'll be able to reply to any questions.
Abigail
richardleach
Migrated from rt.perl.org#32331 (status was 'open')
Searchable as RT32331$