This presentation was created for, and presented at, the August 11th Thousand Oaks Perl Mongers meeting.

1. MooseBest Practices by Aran Deltac (CPAN: bluefeet)

2. make_immutable() package MyClass; use Moose; … __PACKAGE__->meta->make_immutable; 1;

3. default => $value has ‘is_clean’ => ( is => ‘ro’, isa => ‘Bool’, default => 1, );

4. Many Possible States has ‘ages’ => ( is => ‘rw’, isa => ‘ArrayRef’, ); sub avg_age { my ($self) = @_; my $ages = $self->ages(); return (sum @$ages ) / scalar @$ages; } Possible States: undef [] [ … ] if (defined($ages) and @$ages) { … }

5. Many Possible States has ‘ages’ => ( is => ‘rw’, isa => ‘ArrayRef’, default => sub{ [] }, ); sub avg_age { my ($self) = @_; my $ages = $self->ages(); return (sum @$ages ) / scalar @$ages; } Possible Values: undef [] [ … ] if (@$ages) { … }

6. required => 1 has ‘ssn’ => ( is => ‘ro’, isa => ‘Str’, required => 1, );

7. Many Possible States subtype ‘NonEmptyArrayRef' => as ‘ArrayRef’ => where { @$_ > 0 }; has ‘ages’ => ( is => ‘rw’, isa => ‘NonEmptyArrayRef’, required => 1, ); sub avg_age { my ($self) = @_; my $ages = $self->ages(); return (sum @$ages ) / scalar @$ages; } Possible Values: undef [] [ … ] …

8. builder => $sub_name has ‘dbh’ => ( is => ‘ro’, isa => ‘dbh’, builder => ‘_build_dbh’, ); sub _build_dbh { return DBI->connect(…); }

9. lazy => $bool has ‘dbh’ => ( is => ‘ro’, isa => ‘dbh’, builder => ‘_build_dbh’, lazy => 1, ); sub _build_dbh { return DBI->connect(…); }

10. lazy_build => 1 has ‘dbh’ => ( is => ‘ro’, isa => ‘DBI::db’, lazy_build => 1, ); sub _build_dbh { return DBI->connect( … ); }

11. is => ‘ro’ has ‘name’ => ( is => ‘ro’, isa => ‘Str’, );

12. Changing State has ‘ages’ => ( is => ‘rw’, isa => ‘ArrayRef’, default => sub{ [] }, ); has ‘avg_age’ => ( is => ‘ro’, isa => ‘Int’, lazy_build => 1, ); sub _build_avg_age { my ($self) = @_; my $ages = $self->ages(); return (sum @$ages ) / scalar @$ages; } my $obj = Class->new( ages => [4, 7], ); print $obj->avg_age(); # 6 $obj->ages([4, 11]); print $obj->avg_age(); # 6!

13. Changing State has ‘ages’ => ( is => ‘ro’, isa => ‘ArrayRef’, default => sub{ [] }, ); has ‘avg_age’ => ( is => ‘ro’, isa => ‘Int’, lazy_build => 1, ); sub _build_avg_age { my ($self) = @_; my $ages = $self->ages(); return (sum @$ages ) / scalar @$ages; } my $obj = Class->new( ages => [4, 7], ); print $obj->avg_age(); # 6 $obj->ages([4, 11]); print $obj->avg_age(); # 6!

14. writer => $sub_name has ‘color’ => ( is => ‘ro’, isa => ‘Str’, write => ‘_color’, );

15. init_arg => undef has ‘result’ => ( is => ‘ro’, isa => ‘HashRef’, writer => ‘_set_result’, init_arg => undef, );