Moose::Cookbook::Snack::Types(3pm)

SYNOPSIS

  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";
  }

DESCRIPTION

This is the Point example from Moose::Cookbook::Basics::Point_AttributesAndSubclassing 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.

SEE ALSO

Moose::Cookbook::Basics::Point_AttributesAndSubclassing

Moose::Util::TypeConstraints

Moose::Meta::Attribute