Type::Tiny » Manual » UsingWithMoose

how to use Type::Tiny with Moose

First read Type::Tiny::Manual::Moo, Type::Tiny::Manual::Moo2, and Type::Tiny::Manual::Moo3. Everything in those parts of the manual should work exactly the same in Moose.

This part of the manual will focus on Moose-specifics.

Why Use Type::Tiny At All?

Moose does have a built-in type constraint system which is fairly convenient to use, but there are several reasons you should consider using Type::Tiny instead.

  • Type::Tiny type constraints will usually be faster than Moose built-ins. Even without Type::Tiny::XS installed, Type::Tiny usually produces more efficient inline code than Moose. Coercions will usually be a lot faster.
  • Type::Tiny provides helpful methods like where and plus_coercions that allow type constraints and coercions to be easily tweaked on a per-attribute basis.

    Something like this is much harder to do with plain Moose types:

      has name => (
        is      => "ro",
        isa     => Str->plus_coercions(
          ArrayRef[Str], sub { join " ", @$_ },
        coerce  => 1,

    Moose tends to encourage defining coercions globally, so if you wanted one Str attribute to be able to coerce from ArrayRef[Str], then all Str attributes would coerce from ArrayRef[Str], and they'd all do that coercion in the same way. (Even if it might make sense to join by a space in some places, a comma in others, and a line break in others!)

  • Type::Tiny provides automatic deep coercions, so if type Xyz has a coercion, the following should "just work":
      isa xyzlist => ( is => 'ro', isa => ArrayRef[Xyz], coerce => 1 );
  • Type::Tiny offers a wider selection of built-in types.
  • By using Type::Tiny, you can use the same type constraints and coercions for attributes and method parameters, in Moose and non-Moose code.


If you've used Moose::Util::TypeConstraints, you may be accustomed to using a DSL for declaring type constraints:

  use Moose::Util::TypeConstraints;
  subtype 'Natural',
    as 'Int',
    where { $_ > 0 };

There's a module called Type::Utils that provides a very similar DSL for declaring types in Type::Library-based type libraries.

  package My::Types {
    use Type::Library -base;
    use Type::Utils;
    use Types::Standard qw( Int );
    declare 'Natural',
      as Int,
      where { $_ > 0 };

Personally I prefer the more object-oriented way to declare types though.

Since Type::Library 1.012, a shortcut has been available for importing Type::Library and Type::Utils at the same time:

  package MyType {
    use Type::Library -base, -utils;

In Moose you might also declare types like this within classes and roles too. Unlike Moose, Type::Tiny doesn't keep types in a single global flat namespace, so this doesn't work quite the same with Type::Utils. It still creates the type, but it doesn't store it in any type library; the type is returned.

  package My::Class {
    use Moose;
    use Type::Utils;
    use Types::Standard qw( Int );
    my $Natural =          # store type in a variable
      declare 'Natural',
      as Int,
      where { $_ > 0 };
    has number => ( is => 'ro', isa => $Natural );

But really, isn't the object-oriented way cleaner?

  package My::Class {
    use Moose;
    use Types::Standard qw( Int );
    has number => (
      is   => 'ro',
      isa  => Int->where('$_ > 0'),

Type::Tiny and MooseX::Types

Types::Standard should be a drop-in replacement for MooseX::Types. And Types::Common::Numeric and Types::Common::String should easily replace MooseX::Types::Common::Numeric and MooseX::Types::Common::String.

That said, if you do with to use a mixture of Type::Tiny and MooseX::Types, they should fit together pretty seamlessly.

  use Types::Standard qw( ArrayRef );
  use MooseX::Types::Common::Numeric qw( PositiveInt );
  # this should just work
  my $list_of_nums = ArrayRef[PositiveInt];
  # and this
  my $list_or_num = ArrayRef | PositiveInt;

-moose Import Parameter

If you have read this far in the manual, you will know that this is the usual way to import type constraints:

  use Types::Standard qw( Int );

And the Int which is imported is a function that takes no arguments and returns the Int type constraint, which is a blessed object in the Type::Tiny class.

Type::Tiny mocks the Moose::Meta::TypeConstraint API so well that most Moose and MooseX code will not be able to tell the difference.

But what if you need a real Moose::Meta::TypeConstraint object?

  use Types::Standard -moose, qw( Int );

Now the Int function imported will return a genuine native Moose type constraint.

This flag is mostly a throwback from when Type::Tiny native objects didn't directly work in Moose. In 99.9% of cases, there is no reason to use it and plenty of reasons not to. (Moose native type constraints don't offer helpful methods like plus_coercions and where.)

moose_type Method

Another quick way to get a native Moose type constraint object from a Type::Tiny object is to call the moose_type method:

  use Types::Standard qw( Int );
  my $tiny_type   = Int;
  my $moose_type  = $tiny_type->moose_type;

Internally, this is what the -moose flag makes imported functions do.

Next Steps

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