=encoding utf-8

=head1 NAME

Type::Tiny::Manual::UsingWithMouse - how to use Type::Tiny with Mouse

=head1 MANUAL

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

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

Overall, Type::Tiny is less well-tested with Mouse than it is with
Moose and Moo, but there are still a good number of test cases for
using Type::Tiny with Mouse, and there are no known major issues
with Type::Tiny's Mouse support.

=head2 Why Use Type::Tiny At All?

Mouse 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.


=item *

Type::Tiny provides helpful methods like C<where> and C<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 Mouse types:

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

Mouse tends to encourage defining coercions globally, so if you wanted
one B<Str> attribute to be able to coerce from B<< ArrayRef[Str] >>, then
I<all> B<Str> attributes would coerce from B<< 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

=item *

Type::Tiny provides automatic deep coercions, so if type B<Xyz> has a coercion,
the following should "just work":

  isa xyzlist => ( is => 'ro', isa => ArrayRef[Xyz], coerce => 1 );

=item *

Type::Tiny offers a wider selection of built-in types.

=item *

By using Type::Tiny, you can use the same type constraints and coercions
for attributes and method parameters, in Mouse and non-Mouse code.


=head2 Type::Utils

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

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

There's a module called L<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.

In Mouse you might also declare types like this within classes and roles too.
Unlike Mouse, 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 Mouse;
    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 Mouse;
    use Types::Standard qw( Int );
    has number => (
      is   => 'ro',
      isa  => Int->where('$_ > 0'),

=head2 Type::Tiny and MouseX::Types

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

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

  use Types::Standard qw( ArrayRef );
  use MouseX::Types::Mouse qw( Int );
  # this should just work
  my $list_of_nums = ArrayRef[Int];
  # and this
  my $list_or_num = ArrayRef | Int;

=head2 C<< -mouse >> 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 C<Int> which is imported is a function that takes no arguments and
returns the B<Int> type constraint, which is a blessed object in the
L<Type::Tiny> class.

Type::Tiny mocks the L<Mouse::Meta::TypeConstraint> API so well that most
Mouse and MouseX code will not be able to tell the difference.

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

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

Now the C<Int> function imported will return a genuine native Mouse type

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

=head2 C<< mouse_type >> Method

Another quick way to get a native Mouse type constraint object from a
Type::Tiny object is to call the C<mouse_type> method:

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

Internally, this is what the C<< -mouse >> flag makes imported functions

=head2 Type::Tiny Performance

Type::Tiny should run pretty much as fast as Mouse types do. This is
because, when possible, it will use Mouse's XS implementations of type
checks to do the heavy lifting.

There are a few type constraints where Type::Tiny prefers to do things
without Mouse's help though, for consistency and correctness. For example,
the Mouse XS implementation of B<Bool> is... strange... it accepts blessed
objects that overload C<bool>, but only if they return false. If they return
true, it's a type constraint error.

Using Type::Tiny instead of Mouse's type constraints shouldn't make a
significant difference to the performance of your code.


Here's your next step:


=item * L<Type::Tiny::Manual::UsingWithClassTiny>

Including how to Type::Tiny in your object's C<BUILD> method, and
third-party shims between Type::Tiny and Class::Tiny.


=head1 AUTHOR

Toby Inkster E<lt>tobyink@cpan.orgE<gt>.


This software is copyright (c) 2013-2014, 2017-2021 by Toby Inkster.

This is free software; you can redistribute it and/or modify it under
the same terms as the Perl 5 programming language system itself.