It's not a question of lack of access. You wrap the function that gets the value to assign to "n", which means the value hasn't been assigned to "n" yet.

$self->{n} = sub {
   my ($self) = @_;
   my $rv = $self->do_n();
   $self->do_n2();
   return $rv;
}->();
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Now sure how to fix your problem since you didn't specify what you wanted to do. Perhaps

#!/usr/bin/perl -w
use strict;

{
   package Test;
   use Mouse;

   has 'n'  => ( is => 'rw', isa => 'Int', default => 3 );
   has 'n2' => ( is => 'rw', isa => 'Int', lazy => 1,
       default => sub { $_[0]->n + 1 } );

   __PACKAGE__->meta->make_immutable();
}

my $test = Test->new();
print($test->n,  "\n");  # 3
print($test->n2, "\n");  # 4
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