Moose::Cookbook::Snack::Types - Snippets of code for using Types and Type Constraints

version 2.0010

  package Point;
  use Moose;

  has 'x' => ( isa => 'Int', is => 'ro' );
  has 'y' => ( isa => 'Int', is => 'rw' );

  package main;
  use Try::Tiny;

  my $point = try {
      Point->new( x => 'fifty', y => 'forty' );
  }
  catch {
      print "Oops: $_";
  };

  my $point;
  my $xval             = 'forty-two';
  my $xattribute       = Point->meta->find_attribute_by_name('x');
  my $xtype_constraint = $xattribute->type_constraint;

  if ( $xtype_constraint->check($xval) ) {
      $point = Point->new( x => $xval, y => 0 );
  }
  else {
      print "Value: $xval is not an " . $xtype_constraint->name . "\n";
  }

This is the Point example from Moose::Cookbook::Basics::Recipe1 with type checking added.

If we try to assign a string value to an attribute that is an Int, Moose will die with an explicit error message. The error will include the attribute name, as well as the type constraint name and the value which failed the constraint check.

We use Try::Tiny to catch this error message.

Later, we get the Moose::Meta::TypeConstraint object from a Moose::Meta::Attribute and use the Moose::Meta::TypeConstraint to check a value directly.

Moose::Cookbook::Basics::Recipe1

Moose::Utils::TypeConstraints

Moose::Meta::Attribute

Stevan Little <stevan@iinteractive.com>

This software is copyright (c) 2011 by Infinity Interactive, Inc..

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