Don't use $_ when checking member constraints, since that can conflict with $_ used...

[gitmo/Moose.git] / lib / Moose / Cookbook / Snack / Types.pod

package Moose::Cookbook::Snack::Types;

# ABSTRACT: Snippets of code for using Types and Type Constraints

__END__


=pod

=head1 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";
  }

=head1 DESCRIPTION

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

If we try to assign a string value to an attribute that is an C<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 L<Try::Tiny> to catch this error message.

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

=head1 SEE ALSO

=over 4

=item L<Moose::Cookbook::Basics::Recipe1>

=item L<Moose::Utils::TypeConstraints>

=item L<Moose::Meta::Attribute>

=back

=cut