PHP 訪問者模式

目的

訪問者模式允許將對(duì)象上的操作外包給其他對(duì)象。這樣做的主要原因是保持關(guān)注數(shù)據(jù)結(jié)構(gòu)和數(shù)據(jù)操作的分離。但是類必須定義一個(gè)允許訪問的契約(示例中的Role::accept方法)。

契約是一個(gè)抽象類，但你也可以就是一個(gè)接口。在這種情況下，每個(gè)Visitor必須自己選擇要調(diào)用哪個(gè)方法。

UML 圖

代碼

RoleVisitor.php

<?php

declare(strict_types=1);

namespace DesignPatterns\Behavioral\Visitor;

/**
 * Note: the visitor must not choose itself which method to
 * invoke, it is the visited object that makes this decision
 */
interface RoleVisitor
{
    public function visitUser(User $role);

    public function visitGroup(Group $role);
}

RecordingVisitor.php

<?php

declare(strict_types=1);

namespace DesignPatterns\Behavioral\Visitor;

class RecordingVisitor implements RoleVisitor
{
    /**
     * @var Role[]
     */
    private array $visited = [];

    public function visitGroup(Group $role)
    {
        $this->visited[] = $role;
    }

    public function visitUser(User $role)
    {
        $this->visited[] = $role;
    }

    /**
     * @return Role[]
     */
    public function getVisited(): array
    {
        return $this->visited;
    }
}

Role.php

<?php

declare(strict_types=1);

namespace DesignPatterns\Behavioral\Visitor;

interface Role
{
    public function accept(RoleVisitor $visitor);
}

User.php

<?php

declare(strict_types=1);

namespace DesignPatterns\Behavioral\Visitor;

class User implements Role
{
    public function __construct(private string $name)
    {
    }

    public function getName(): string
    {
        return sprintf('User %s', $this->name);
    }

    public function accept(RoleVisitor $visitor)
    {
        $visitor->visitUser($this);
    }
}

Group.php

<?php

declare(strict_types=1);

namespace DesignPatterns\Behavioral\Visitor;

class Group implements Role
{
    public function __construct(private string $name)
    {
    }

    public function getName(): string
    {
        return sprintf('Group: %s', $this->name);
    }

    public function accept(RoleVisitor $visitor)
    {
        $visitor->visitGroup($this);
    }
}

測試

Tests/VisitorTest.php

<?php

declare(strict_types=1);

namespace DesignPatterns\Tests\Visitor\Tests;

use DesignPatterns\Behavioral\Visitor\RecordingVisitor;
use DesignPatterns\Behavioral\Visitor\User;
use DesignPatterns\Behavioral\Visitor\Group;
use DesignPatterns\Behavioral\Visitor\Role;
use DesignPatterns\Behavioral\Visitor;
use PHPUnit\Framework\TestCase;

class VisitorTest extends TestCase
{
    private RecordingVisitor $visitor;

    protected function setUp(): void
    {
        $this->visitor = new RecordingVisitor();
    }

    public function provideRoles()
    {
        return [
            [new User('Dominik')],
            [new Group('Administrators')],
        ];
    }

    /**
     * @dataProvider provideRoles
     */
    public function testVisitSomeRole(Role $role)
    {
        $role->accept($this->visitor);
        $this->assertSame($role, $this->visitor->getVisited()[0]);
    }
}