Perhaps because it's not clear how much a win this will be?
Copying a scalar requires making a new scalar. Making a ref
also requires making a new scalar. There might be a small
win, but it's probably dwarved by the expensive_func call.
The following benchmark shows that the gain is small:
#!/usr/bin/perl
use strict;
use warnings;
use Benchmark qw /cmpthese/;
our @array = map {sprintf "aaa:%03d" => $_} 0 .. 999;
our (@a, @b);
for (my $i = @array; -- $i;) {
my $j = rand ($i + 1);
@array [$i, $j] = @array [$j, $i];
}
cmpthese -5 => {
ST => '@::a = map {$_ -> [0]}
sort {$a -> [1] <=> $b -> [1]}
map {[$_ => substr $_, 4]} @array',
Liz => '@::b = map {${$_ -> [0]}}
sort {$a -> [1] <=> $b -> [1]}
map {[\$_ => substr $_, 4]} @array',
};
foreach my $i (0 .. 999) {
die unless $a [$i] eq $b [$i];
}
__END__
Benchmark: running Liz, ST for at least 5 CPU seconds...
Liz: 5 wallclock secs ( 5.31 usr + 0.00 sys = 5.31 CPU) @ 10
+2.45/s (n=544)
ST: 5 wallclock secs ( 5.37 usr + 0.00 sys = 5.37 CPU) @ 10
+5.40/s (n=566)
Rate Liz ST
Liz 102/s -- -3%
ST 105/s 3% --
Although you might know cases where there is a bigger gain.
Abigail
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