58_logger.pl

package Logger;
use Moose;

has 'fout', is => 'ro', lazy_build => 1;
has 'filename', is => 'ro';

sub _build_fout {
    my $self = shift;
    my $fh;


    if ( $self->filename ) {
        open $fh, '>', $self->filename;
    } else {
        $fh = *STDOUT;
    }

    return $fh;
}

sub log {
    my $self = shift;
    my $fh = $self->fout;
    print $fh @_, "\n";
}

sub DEMOLISH {
    my $self = shift;
    close $self->fout if $self->fout;
}

package main;

# Dependency injection
my $test;
open my $fake_fout, '>', \$test;

my $l2 = Logger->new( fout => $fake_fout );
$l2->log("Hello");

die "Fail" if $test ne "Hello\n";

close $fake_fout;