Hello wise ones. I'm playing around with Moose, with a view to using a class to represent an XML element and ultimately to generate the XML itself. The below code works but I am not entirely happy with the use of the predicate method to determine if each attribute (the majority of which are optional) needs to be included in the resulting XML. Is there a better way I can approach this? I have considered trigger and after methods to record the attributes that have been set but both feel equally clumsy. Many thanks. 
package Button;
use Moose;
use namespace::autoclean;
use XML::Writer;

has 'name'  => ( is => 'rw', isa => 'Str', required => 1);
has 'x' => ( is => 'rw', isa => 'Int', predicate => 'has_x');
has 'y' => ( is => 'rw', isa => 'Int', predicate => 'has_y');
has 'w' => ( is => 'rw', isa => 'Int', predicate => 'has_w');
has 'h' => ( is => 'rw', isa => 'Int', predicate => 'has_h');

sub to_xml {

    my ($self) = @_;
    
    my %attr;
    $attr{name} = $self->name;
    $attr{x} = $self->x if $self->has_x;
    $attr{y} = $self->y if $self->has_y;
    $attr{w} = $self->w if $self->has_w;
    $attr{h} = $self->h if $self->has_h;
    
    my $writer = XML::Writer->new( OUTPUT => 'self' );
    $writer->emptyTag('button', %attr);
    
    return $writer->to_string;
}

__PACKAGE__->meta->make_immutable;

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In reply to Moose attribute predicate alternative by antmico

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