The following map variant works out significantly faster than the previously posted map variants, though not as fast as for-loop based variants:
sub variation3ep {
my $idx = -1;
my %hash = map(($_ => ++$idx), @array);
}
While the block form of map is often favoured for its clarity, the expression form of map is faster because it avoids the overhead of creating a lexical pad.
This is actually another reason why BrowserUk's variation4 is fast - he uses the for statement modifier rather than a for loop with a block. Compare:
#!/usr/bin/env perl
use strict;
use warnings;
use Benchmark qw(:all);
my @array='aa' .. 'zz';
sub variation4 {
my $idx = 0;
my %hash; $hash{ $_ } = $idx++ for @array;
}
sub variation5 {
my $idx = 0;
my %hash;
for (@array) {
$hash{ $_ } = $idx++;
}
}
cmpthese(-3, {
'variation4' => \&variation4,
'variation5' => \&variation5,
});
__END__
Rate variation5 variation4
variation5 740/s -- -4%
variation4 773/s 5% --
Yes, it's a small difference, but it's pretty consistently observable.
The absolute fastest I've been able to achieve is a small variation on BrowserUk's variation4 using the prefix increment rather than postfix increment:
sub variation6 {
my $idx = -1;
my %hash; $hash{ $_ } = ++$idx for @array;
}
It seems to give you about a 6% speed up.
perl -E'sub Monkey::do{say$_,for@_,do{($monkey=[caller(0)]->[3])=~s{::}{ }and$monkey}}"Monkey say"->Monkey::do'
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