MooX::StrictConstructor(3) Make your Moo-based object constructors blow up on unknown attributes.


version 0.008


package My::Class;
use Moo;
use MooX::StrictConstructor;
has 'size' => ( is => 'rw');
# then somewhere else, when constructing a new instance
# of My::Class ...
# this blows up because color is not a known attribute
My::Class->new( size => 5, color => 'blue' );


Simply loading this module makes your constructors ``strict''. If your constructor is called with an attribute init argument that your class does not declare, then it dies. This is a great way to catch small typos.


Most of this package was lifted from MooX::InsideOut and most of the Role that implements the strictness was lifted from MooseX::StrictConstructor.


MooseX::StrictConstructor documents two tricks for subverting strictness and avoid having problematic arguments cause an exception: handling them in BUILD or handle them in BUILDARGS.

In MooX::StrictConstructor you can use a BUILDARGS function to handle them, e.g. this will allow you to pass in a parameter called ``spy'' without raising an exception. Useful? Only you can tell.

   sub BUILDARGS {
       my ($self, %params) = @_;
       my $spy delete $params{spy};
       # do something useful with the spy param
       return \%params;

Because "BUILD" methods are run after an object has been constructed and this code runs before the object is constructed the "BUILD" trick will not work.



A class that uses MooX::StrictConstructor but extends another class that does not will not be handled properly. This code hooks into the constructor as it is being strung up (literally) and that happens in the parent class, not the one using strict.

A class that inherits from a Moose based class will discover that the Moose class's attributes are disallowed. Given sufficient Moose meta knowledge it might be possible to work around this. I'd appreciate pull requests and or an outline of a solution.

Subverting strictness

MooseX::StrictConstructor documents a trick for subverting strictness using BUILD. This does not work here because strictness is enforced in the early stage of object construction but the BUILD subs are run after the objects has been built.

Interactions with namespace::clean

MooX::StrictConstructor creates a "new" method that namespace::clean will over-zealously clean. Workarounds include using MooX::StrictConstructor after namespace::autoclean or telling namespace::clean to ignore "new" with something like:

  use namespace::clean -except => ['new','meta'];


George Hartzell <[email protected]>


This software is copyright (c) 2015 by George Hartzell.

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