I don't understand this code, perl delegates and empty parameter lists.

MidasTouch has asked for the wisdom of the Perl Monks concerning the following question:

This is an attribute which belongs to a class that inherits from Moo

has '_print' => (
    is      => 'ro',
    default => sub { Slic3r::Print->new },
    handles => [qw(apply_config extruders          expanded_output_fil
+epath                     total_used_filament total_extruded_volume
                    placeholder_parser process)],
);
[download]

This is the code for Slic3r::Print->new

sub new {
    # TODO: port PlaceholderParser methods to C++, then its own constr
+uctor
    # can call them and no need for this new() method at all
    my ($class) = @_;
    my $self = $class->_new;
    $self->placeholder_parser->apply_env_variables;
    $self->placeholder_parser->update_timestamp;
    return $self;
}
[download]

1. _print doesn't pass any parameters, so what is $class supposed to be assigned? I'm guessing the object which calls the method? 2. _new, haven't been able to find the relevant code for this subroutine. If Simple inherits from Moo::Object then it's in a file with package Moo::Object, right? Or is there some other possibility? 3. placeholder_parser. There is no placeholder_parser subroutine definition in the entire directory for the program or the Perl library. So, what exactly is it doing? Also, if self refers to the Simple object, then how is it calling the delegate before Print->new has returned a value? Thanks

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Re: I don't understand this code, perl delegates and empty parameter lists. by marto (Cardinal) on Mar 20, 2015 at 09:18 UTC
"3. placeholder_parser. There is no placeholder_parser subroutine definition in the entire directory for the program or the Perl library. So, what exactly is it doing?" A quick search shows this among the results: `has 'placeholder_parser' => (is => 'rw', default => sub { Slic3r::GCod +e::PlaceholderParser->new });` [download]	[reply] [d/l]
Re^2: I don't understand this code, perl delegates and empty parameter lists. by MidasTouch (Initiate) on Mar 20, 2015 at 09:45 UTC
Oh okay, that makes sense.	[reply]
Re: I don't understand this code, perl delegates and empty parameter lists. by Anonymous Monk on Mar 20, 2015 at 09:09 UTC
1. _print doesn't pass any parameters, so what is $class supposed to be assigned? When you add "print @_" what gets printed? Have you read perlobj?	[reply]
Re^2: I don't understand this code, perl delegates and empty parameter lists. by MidasTouch (Initiate) on Mar 20, 2015 at 09:44 UTC
So then what is _new calling? Print doesn't seem to inherit any classes. Here is the code https://github.com/alexrj/Slic3r/blob/master/lib/Slic3r/Print.pm	[reply]
Re: I don't understand this code, perl delegates and empty parameter lists. by Anonymous Monk on Mar 20, 2015 at 09:12 UTC
There is no placeholder_parser subroutine definition in the entire directory for the program or the Perl library. So, what exactly is it doing? What file where (got link/url)?	[reply]
Re^2: I don't understand this code, perl delegates and empty parameter lists. by MidasTouch (Initiate) on Mar 20, 2015 at 09:17 UTC
https://github.com/alexrj/Slic3r	[reply]
Re: I don't understand this code, perl delegates and empty parameter lists. by Anonymous Monk on Mar 20, 2015 at 09:08 UTC
A class that inherits from Moo? Weird	[reply]
Re^2: I don't understand this code, perl delegates and empty parameter lists. by MidasTouch (Initiate) on Mar 20, 2015 at 09:15 UTC
>A class that inherits from Moo? Weird well it uses Moo, so it inherits from Moo:Object right? btw how do I make newlines on this forum?	[reply]
Re^3: I don't understand this code, perl delegates and empty parameter lists. by marto (Cardinal) on Mar 20, 2015 at 09:21 UTC
Welcome, this explains the basics of formatting and post conventions.	[reply]
Re^3: I don't understand this code, perl delegates and empty parameter lists. by Anonymous Monk on Mar 20, 2015 at 09:39 UTC
well it uses Moo, so it inherits from Moo:Object right? Well, pretend that Moo::Object doesn't exist :) thats stuff for Moo.pm not you and me:)	[reply]
Re^4: I don't understand this code, perl delegates and empty parameter lists. by MidasTouch (Initiate) on Mar 20, 2015 at 11:04 UTC
Re^5: I don't understand this code, perl delegates and empty parameter lists. by choroba (Cardinal) on Mar 20, 2015 at 12:20 UTC