use strict;
use warnings;

use Data::Dumper;

my $data = str2data('foo[1].bar.baz[0]', 123);
print Dumper($data), "\n";

sub str2data {
    my($string, $value) = @_;
    my $r = \my $return;
    $r = $1 ? \$$r->{$1} : \$$r->[$2]
       while $string =~ /\G(?:\.?(\w+)|\[(\d+)\])/g;
    $$r = $value;
    $return;
}