Using Perl/Moose, what happens to the value returned by modifiers?

Question

Learning perl I just recently discovered the wonders of Moose!

I'm trying to wrap my head around modifiers -- or at least how the return values are handled... do they get stored someplace?

{package Util::Printable;

use Moose::Role;

  requires 'to_str','init';

  before 'to_str' => sub {
      my($self) = @_;
      $self->{to_string} = "my string thing";
      return $self->{to_string}; 
  };

  after 'init' => sub{
    my($self) = @_;
    $self->{roles} = __PACKAGE__;
    $self->{is_printable} = 1;
  };


}
1;
__END__

Using the Printable Role

{package MonkeyPrint;
use Moose;

with 'Util::Printable';


  sub init{
    my($self) = @_;
    return 1;
  };

  sub BUILD{
    my($self) = @_;
    $self->init();  
  }


  # ------------------------------------------------------------------------ # 
  # Printable Support
  # ------------------------------------------------------------------------ #
  use overload '""' => 'to_str';  

  sub to_str {
      my($self) = @_;
      $self->{to_string} = __PACKAGE__;
      return $self->{to_string}; 
  };


 __PACKAGE__->meta->make_immutable;
}
1;
__END__

Cosmetic note: you don't need braces around your `package` block. `package` means "all that comes after will be in such package." As you'll usually stick to a single package per file, there'll be no anbiguity. Note that since 5.14 you can also use a `package Util::Printable { contents }` syntax that's more in line with the other namespaced curly-bracket languages. Whether the new syntax will displace the current common practice is yet to observe. — JB., Sep 13 '11 at 21:43

score 6 · Accepted Answer · answered Sep 13 '11 at 22:14

Say a method has a before and an after wrapper.

The before code is called.
Its return value is ignored/discarded.
The original method is called.
It's value is saved.
The after code is called.
Its return value is ignored/discarded.
The saved value is returned.

Use around if you need to alter or replace the value returned by the original method.

Using Perl/Moose, what happens to the value returned by modifiers?

1 Answers1