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[solved] Help! Overloading operators doesn't work

by mascip (Pilgrim)
on Sep 01, 2012 at 11:14 UTC ( #991143=perlquestion: print w/ replies, xml ) Need Help??
mascip has asked for the wisdom of the Perl Monks concerning the following question:

* Edit : Solved. It was because of namespace::autoclean => i'll use namespace::sweep instead.

None of the operators overloading work in this simple example. What did i do wrong? Probably a simple stupid mistake...
Here is the code (Percent class, followed by very simple script), and the printed output is in comments.

#!/usr/bin/perl use 5.012003; # Perl version requirement #=========================================================== # Percentage CLASS (script below) #=========================================================== package Percentage; use Any::Moose; use namespace::autoclean; has 'int' => ( is => 'ro', isa => 'Int', ); around BUILDARGS => sub { my $orig = shift; my $class = shift; print "build\n"; return $class->$orig(int => @_); }; use overload q{""} => \&to_string, '0+' => \&to_num, '+' => \&add; sub to_string { my $self = shift; print "to_string()\n"; return $self->int(); } sub to_num { my $self = shift; print "to_num()\n"; return $self->int(); } sub add { my ($left, $right) = @_; print "add()\n"; my $result = new Percentage( $left->int() + $right->int() ); return $result; } __PACKAGE__->meta->make_immutable; 1; #=========================================================== # SCRIPT #=========================================================== package Example::Script; use 5.012003; # Perl version requirement use strict; use warnings; # printed in output : my $a = new Percentage(2); # build print "$a\n"; # Percentage=Hash(0x11cfe8c) my $a_num = $a->int(); # my $a_str = "$a"; # print "$a_str, $a_num\n"; # Percentage=Hash(0x11cfe8c), 2 my $b = new Percentage(3); # build my $c = $b + $a; # print "$b, $c\n"; # Percentage=Hash(0x116912c), 3693356

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Re: Help! Overloading operators doesn't work
by Corion (Pope) on Sep 01, 2012 at 11:30 UTC

    Have you tried taking Moose and namespace::autoclean out of the picture?

    Once I remove them and fix the remaining code, it works:

    #!/usr/bin/perl use 5.012003; # Perl version requirement #=========================================================== # Percentage CLASS (script below) #=========================================================== package Percentage; #use Any::Moose; #use namespace::autoclean; sub new { my $class = shift; bless { int => @_ } => $class; }; use overload q{""} => \&to_string, '0+' => \&to_num, '+' => \&add; sub to_string { my $self = shift; print "to_string()\n"; return $self->int(); } sub to_num { my $self = shift; print "to_num()\n"; return $self->int(); } sub add { my ($left, $right) = @_; print "add()\n"; my $result = new Percentage( $left->int() + $right->int() ); return $result; } sub int { $_[0]->{int} } 1; #=========================================================== # SCRIPT #=========================================================== package Example::Script; use 5.012003; # Perl version requirement use strict; use warnings; # printed in output : my $a = new Percentage(2); # build my $a_num = $a->int(); # print "$a\n"; # Percentage=Hash(0x11cfe8c) print "$a, $a_num\n"; # Percentage=Hash(0x11cfe8c), 2 my $b = new Percentage(3); # build my $c = $b + $a; # print "$b, $c\n"; # Percentage=Hash(0x116912c), 3693356 __END__ to_string() 2 to_string() 2, 2 add() to_string() to_string() 3, 5

    I assume that something somewhere within Moose(::Any) or namespace::autoclean messes up the overloading. Maybe the bug reports or feature limitations tell a clearer story.

    Update: Searching Moose for overload points me to Class::MOP::Class, which has an API to introspect overloading. Maybe consult that to find out whether your class actually has overloading, or maybe Moose / MOP want you to set up all your overloading through this mechanism instead of overload directly.

      You're right, it's because of namespace::autoclean

      There is an example in the Moose Cookbook, of overloading with Moose : http://search.cpan.org/~stevan/Moose/lib/Moose/Cookbook/Basics/Recipe9.pod
      It uses the overloading operator.

      According to a namespace::autoclean review, if you use overloading with Moose you should use namespace::sweep instead of namespace::autoclean : "This pragma was written to address some problems with the excellent namespace::autoclean. In particular, namespace::autoclean will remove special symbols that are installed by overload, so you can't use namespace::autoclean on objects that overload Perl operators."

Re: Help! Overloading operators doesn't work
by philiprbrenan (Monk) on Sep 01, 2012 at 11:37 UTC

    Please tell me where $a_str is declared before it is used in:

    print "$a_str, $a_num\n";

    I cannot get your script to compile without it. Thanks.

      Added, my mistake.

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