Question

I’m currently starting with Perl OOP using the ‘Moose’ package.

The compiler complains that it ‘Can’t modify non-lvalue subroutine call at Parser.pm line 16.’

I don’t quite understand why I can’t just assign a new object. I guess there is a better or more valid way to do optional parameters with Moose?

    #!/usr/bin/perl -w  package Parser;  use Moose;  require URLSpan;  require WWW::Mechanize;  has 'urlspan' => (is => 'rw', isa => 'URLSpan', required => 1); has 'mech' => (is => 'rw', isa => 'WWW::Mechanize');  sub BUILD {     my $self = shift;     if(!$self->mech) {         warn('no Mech set for ' . $self->urlspan->name);         $self->mech = WWW::Mechanize->new(agent => 'Mozilla/5.0 (Windows; U; Windows NT 6.0; de; rv:1.9.0.6) Gecko/2009011913 Firefox/3.0.4',                                          stack_depth => 1                                          ); #line 16         }  } 

Answer 1

$self->mech is a method call; you can’t really treat it like a field in a C struct. If you want to set it, you need to pass the new object to it.

        $self->mech(              WWW::Mechanize->new(                 agent => 'xyz',                 stack_depth => 1             )         );