Moose - two augmented methods in one class

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

I have a subclass extending parent class method via inner() and augment

package C1;
use Moose;

sub html {
    my $this = shift;
    return '<html>' . '<body>' . inner() . '</body>' . '</html>';
}

package C2;
use Moose;

extends 'C1';

augment html => sub { return 'C2'; };
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warn C2->new->html;


# yields
# <html><body>C2</body></html>
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I want to add another augmentable method, which content is not mandatory, i.e. I don't want to supply augment in every subclass.

package C1;
use Moose;

sub html {
    my $this = shift;
    return
          '<html>'
        . $this->head
        . '<body>'
        . inner()
        . '</body>'
        . '</html>';
}

sub head { return '<head>' . (inner() || '') . '</head>'; }

package C2;
use Moose;

extends 'C1';

augment html => sub { return 'C2'; };
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But if I don't supply the content of head method in subclass then the content of html method is used:

warn C2->new->html;

# yields
# <html><head>C2</head><body>C2</body></html>
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So is it possible to use more than one augmentable method, with some of them having "optional" content?

Thanks for any reply including those: "You should not do this, ..."

Roman

Comment on Moose - two augmented methods in one class Select or Download Code

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Re: Moose - two augmented methods in one class by tobyink (Canon) on Jan 09, 2012 at 14:50 UTC
I don't really have any opinion on whether or not you should be doing this, but... package C1; use Moose; sub html { my $this = shift; return '<html>' . $this->head . '<body>' . inner() . '</body>' . '</html>'; } sub head { my $self = shift; my $child_implementation = $self->meta->get_method('head'); my $has_child_implementation = blessed($child_implementation) && $child_implementation->isa('Moose::Meta::Method::Augmented' +); return '<head>' . ($has_child_implementation ? inner() : '') . '</ +head>'; } package C2; use Moose; extends 'C1'; augment html => sub { return 'C2'; }; package main; warn C2->new->html; [download]	[reply] [d/l]
Re^2: Moose - two augmented methods in one class by tobyink (Canon) on Jan 09, 2012 at 15:19 UTC
Replying to myself... you might want to factor out some of that augmentation detection code if you're going to be doing this a lot... package AugmentationDetective; use Moose::Role; sub is_augmented { my ($self, $method_name) = @_; my $method = $self->meta->get_method($method_name); return blessed($method) && $method->isa('Moose::Meta::Method::Augmented'); } package C1; use Moose; with 'AugmentationDetective'; sub html { my $this = shift; return '<html>' . $this->head . '<body>' . inner() . '</body>' . '</html>'; } sub head { my $self = shift; return '<head>'.($self->is_augmented('head')?inner():'').'</head>'; } package C2; use Moose; extends 'C1'; augment html => sub { return 'C2'; }; package main; warn C2->new->html; [download]	[reply] [d/l]
Re^2: Moose - two augmented methods in one class by zwon (Abbot) on Jan 09, 2012 at 15:25 UTC
Update: ignore this, tobyink is right, I didn't pay enough attention to the question This cumbersome check is not really required. `inner` is no-op if there's no `augment`: `use 5.010; use strict; use warnings; { package C1; use Moose; sub test { return "<C1>".(inner()//'')."</C1>"; } } { package C2; use Moose; extends 'C1'; } my $c2 = C2->new; say $c2->test; __END__ <C1></C1>` [download]	[reply] [d/l] [select]
Re^3: Moose - two augmented methods in one class by tobyink (Canon) on Jan 09, 2012 at 15:37 UTC
Actually, in the example, it does seem necessary, as it seems to hit onto a ~~barely documented area of Moose behaviour~~ bug according to several people in #moose in irc.perl.org. The `html` method defined in the superclass, calls `head` defined in the invocant. `head` isn't augmented in the subclass, so the `head` method defined in the superclass is used directly. This calls `inner` which searches up the callstack for an augmented method. While we'd want it to find `head`, that method is not augmented in the subclass, so it finds `html` instead, inadvertently using the wrong augmentation. Try the code from the original question and you'll see.	[reply] [d/l] [select]
Re^4: Moose - two augmented methods in one class by tobyink (Canon) on Jan 09, 2012 at 16:13 UTC
Re^5: Moose - two augmented methods in one class by stvn (Monsignor) on Jan 11, 2012 at 05:19 UTC
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