Perl OO 使用 Moose - 编写委托(delegate)示例的最佳方式？

Question

Perl 的 Moose 与其他对象系统不同，因此如何将其他语言已知的示例翻译成 Moose 术语并不总是很清楚。考虑以下 Rectangle 和 Square 的 Java 示例，其中 Square 实例(正方形是特殊的矩形)将对 area() 的调用委托(delegate)给它持有私有(private)引用的 Rectangle 实例。

package geometry;
class Rectangle {
    private int x;
    private int y;
    public Rectangle(int x, int y) {
        this.x = x;
        this.y = y;
    }
    public int area() {
        return x * y;
    }
}
class Square {
    private Rectangle rectangle;
    public Square(int a) {
        this.rectangle = new Rectangle(a, a);
    }
    public int area() {
        return this.rectangle.area();
    }
}
public class Main {
    public static void main( String[] args ) {
        int x, y;
        if ( args.length > 1 ) {
            x = Integer.parseInt( args[0] );
            y = Integer.parseInt( args[1] );
        }
        else {
            x = 3;
            y = 7;
        }
        Rectangle r = new Rectangle( x, y );
        System.out.println( r.area() );
        Square sq1 = new Square( x );
        System.out.println( sq1.area() );
        Square sq2 = new Square( y );
        System.out.println( sq2.area() );
    }
}

我拼凑了以下 Perl/Moose/Mouse 版本，我不确定这是不是正确的做事方式，所以我将其提交给聚集在这些大厅的专家公会的判断:

package Rectangle;
use Mouse;
has [ qw( x y ) ], is => 'ro', isa => 'Int';

sub area {
    my( $self ) = @_;
    return $self->x * $self->y;
}

package Square;
use Mouse;
has x => is => 'ro', isa => 'Int';
has rectangle => is => 'ro', isa => 'Rectangle';

# The tricky part: modify the constructor.
around BUILDARGS => sub {
    my $orig = shift;
    my $class = shift;
    my %args = @_ == 1 ? %{ $_[0] } : @_;
    $args{rectangle} = Rectangle->new( x => $args{x}, y => $args{x} );
    return $class->$orig( \%args );
};

sub area { $_[0]->rectangle->area } # delegating

package main;
use strict;
my $x = shift || 3;
my $y = shift || 7;
my $r = Rectangle->new( x => $x, y => $y);
my $sq1 = Square->new( x => $x );
my $sq2 = Square->new( x => $y );
print $_->area, "\n" for $r, $sq1, $sq2;

这行得通，但由于我没有看到太多 Moose 在行动，我只是不确定这是要走的路，或者是否有更简单的方法。感谢您提供任何反馈，或提供更多 Moose 用户级别讨论的建议。

Answer 1

虽然我不确定这是最佳实践，但我能想到的最佳翻译可能是这样的:

package Rectangle;
use Mouse;
has [ qw( x y ) ], is => 'ro', isa => 'Int';

sub area {
    my( $self ) = @_;
    return $self->x * $self->y;
}

package Square;
use Mouse;
has x => is => 'ro', isa => 'Int';
has rectangle =>
    is => 'ro',
    isa => 'Rectangle',
    lazy_build => 1,
    handles => [ 'area' ];

sub _build_rectangle {
    my $self = shift;
    Rectangle->new(x => $self->x, y => $self->x);
}

handles in rectangle 属性会自动为您建立对区域的委托(delegate)。