CODEWITHSUNDEEP
perl
Håkon Hægland
Håkon Hægland

Reputation: 40718

Returning a string or a string reference using eval modifier

Is there any advantage of returning a reference to the string instead of the string itself when using the e modifier?

For example:

use strict;
use warnings;

my $str1 = my $str2 = "aa bb cc";

$str1 =~ s/\s(bb)\s/${func1($1)}/e;
$str2 =~ s/\s(bb)\s/func2($1)/e;

sub func1 {
    my ($name) = @_;

    my $str = "A large string";
    return \$str;
}

sub func2 {
    my ($name) = @_;

    my $str = "A large string";
    return $str;
}

I am thinking about the case when the returned string is quite large. Will it be more efficient to use a reference?

Upvotes: 2

Views: 58

Answers (1)

ikegami
ikegami

Reputation: 385506

Only benchmarking will tell, but it looks like it.

Returning a scalar usually copies it.

$ perl -MDevel::Peek -e'
   sub f { my $x = 'abc'; Dump($x); $x }  Dump(f());
' 2>&1 | grep -Po 'PV = \K\S*'
0x275d5f0
0x276e270

But not when :lvalue is used.

$ perl -MDevel::Peek -e'
   sub f :lvalue { my $x = 'abc'; Dump($x); $x }  Dump(f());
' 2>&1 | grep -Po 'PV = \K\S*'
0x220bd00
0x220bd00

5.20 introduced copy-on-write strings, so both scalars ($x and the returned one) share the same string buffer until you change one (forcing a copy then).

$ perl -MDevel::Peek -e'
   sub f { my $x = 'abc'; Dump($x); $x }  Dump(f());
' 2>&1 | grep -Po 'PV = \K\S*'
0xda4780
0xda4780

Upvotes: 2

Related Questions