Change context of return of map?

Question

I'm trying to parse a JSON string into an array reference:

my $str = '[[2],[1]]';
my $data = map { $_->[0] } @{decode_json( $str )};

but this makes it a scalar. I can do:

my $str = '[[2],[1]]';
my @data = map { $_->[0] } @{decode_json( $str )};
my $data = \@data;

but it's not as short as I like. any help?

Answer 1

Using an intermediate variable:

my $str = '[[2],[1]]';
my @data = map { $_->[0] } @{decode_json( $str )};
my $data = \@data;

Answer 2

How about:

my $str = '[[2],[1]]';
my $data = [map {$_->[0]} @{decode_json($str)}];

Answer 3

Since the OP asked which approach has more overhead, here's a quick profile I used to compare the two. Feel free to edit the entry with ways to improve the measurement:

#!/usr/bin/perl -w
use strict;
use Benchmark qw(cmpthese);

sub count(\$$) {
    ${$_[0]} += @{$_[1]};
}

sub a() {
    count($a, [map {$_ + 1} 1..1000000]);
}

sub b() {
    my @d = map {$_ + 1} 1..1000000;
    count($b, \@d);
}

cmpthese(-10, {a => \&a, b => \&b});