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Moose Best Practices

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

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

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  • 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,
    );