$self->{tempfile} = File::Temp->new(UNLINK => 1, SUFFIX => '.tmp');
print $self->{tempfile} "I am here";

##</code><code>##

$self->tempfile( File::Temp->new(UNLINK => 1, SUFFIX => '.tmp') );
print {$self->tempfile} "I am here";

##</code><code>##

package test;   # not 'test.pm'
use Moose;
use File::Temp;

has tempfile => (
    is       => 'rw',
    isa      => 'File::Temp',
    lazy     => 1,
    default  => sub {
        File::Temp->new(UNLINK => 1, SUFFIX => '.tmp')
    },
);

sub BUILD {
    my $self = shift;
    print { $self->tempfile } "I am here";
}