Moose::Cookbook::Snack::Types - Snippets of code for using Types and Type Constraints
package Point; use Moose; has 'x' => ( isa => 'Int', is => 'ro' ); has 'y' => ( isa => 'Int', is => 'rw' ); package main; my $point = eval { Point->new( x => 'fifty', y => 'forty' ); }; if ($@) { 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.
Int
We use eval to catch this error message in $@.
eval
$@
Later, we get the Moose::Meta::TypeConstraint object from a Moose::Meta::Attribute and use the Moose::Meta::TypeConstraint to check a value directly.
Jess Robinson <cpan@desert-island.me.uk>
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