NAME

MANUAL

Let's translate the classic Horse class from Moo to Class::Tiny.

Moo:

  package Horse {
    use Moo;
    use Types::Standard qw( Str Num ArrayRef );
    use namespace::autoclean;
    
    has name       => ( is => 'ro', isa => Str, required => 1 );
    has gender     => ( is => 'ro', isa => Str );
    has age        => ( is => 'rw', isa => Num );
    has children   => (
      is       => 'ro',
      isa      => ArrayRef,
      default  => sub { return [] },
    );
  }

Class::Tiny:

  package Horse {
    use Class::Tiny qw( gender age ), {
      name     => sub { die "name is required"; },
      children => sub { return [] },
    };
    use Types::Standard qw( Str Num ArrayRef Dict Optional slurpy Any);
    use Type::Params qw( wrap_methods compile );
    use namespace::autoclean;
    
    # type checks
    wrap_methods(
      BUILD    => [Dict[
        name       => Str,
        gender     => Optional[Str],
        age        => Optional[Num],
        children   => Optional[ArrayRef],
        slurpy Any,
      ]],
      name     => [],
      gender   => [],
      age      => Optional[Num],
      children => [],
    );
  }

What's going on here?

Well, Class::Tiny, after it has built a new object, will do this:

  $self->BUILD($args);

(Technically, it calls "BUILD" not just for the current class, but for all parent classes too.) We can hook onto this in order to check type constraints for the constructor.

We use "wrap_methods" from Type::Params to wrap the original "BUILD" method (which doesn't exist, so "wrap_methods" will just assume an empty sub) with a type check for $args. The type check is just a Dict that checks the class's required and optional attributes and includes slurpy Any at the end to be flexible for subclasses adding new attributes.

Then we wrap the "name", "gender", and "children" methods with checks to make sure they're only being called as getters, and we wrap "age", allowing it to be called as a setter with a Num.

There are also a couple of CPAN modules that can help you out.

  package Horse {
    use Types::Standard qw( Str Num ArrayRef );
    use Class::Tiny::ConstrainedAccessor {
      name     => Str,
      gender   => Str,
      age      => Num,
      children => ArrayRef,
    };
    use Class::Tiny qw( gender age ), {
      name     => sub { die "name is required"; },
      children => sub { return [] },
    };
  }

  package Horse {
    use Class::Tiny::Antlers qw(has);
    use Types::Standard qw( Str Num ArrayRef );
    use namespace::autoclean;
    
    has name       => (
      is        => 'ro',
      isa       => Str,
      default   => sub { die "name is required" },
    );
    has gender     => ( is => 'ro',    isa => Str );
    has age        => ( is => 'rw',    isa => Num );
    has children   => (
      is        => 'ro',
      isa       => ArrayRef,
      default   => sub { return [] },
    );
  }

NEXT STEPS

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Type::Tiny::Manual::UsingWithOther

Using Type::Tiny with Class::InsideOut, Params::Check, and Object::Accessor.

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