Provided by: libtype-tiny-perl_1.008001-2_all bug


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


       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 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.

   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.

       ·   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 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 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 Mouse and non-Mouse code.

       If you've used 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 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'),

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

   "-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 "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 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 "Int" function imported will return a genuine native Mouse type constraint.

       This flag is mostly a throwback from when Type::Tiny native objects 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 "plus_coercions" and

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

         use Types::Standard qw( Int );

         my $tiny_type   = Int;
         my $mouse_type  = $tiny_type->mouse_type;

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

   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
       Bool is... strange... it accepts blessed objects that overload "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:

       ·   Type::Tiny::Manual::UsingWithClassTiny

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


       Toby Inkster <>.


       This software is copyright (c) 2013-2014, 2017-2019 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.