为何Laravel中类继承并实现接口未重写抽象方法？

我了解在PHP里，类继承父类时必须重写所有抽象方法，也可以重写非抽象方法；类实现接口时必须重写接口的所有方法。但在某个Laravel项目里发现例外：子类User继承Authenticatable类并实现MustVerifyEmail接口，却没重写接口里的抽象方法，代码如下：

父接口MustVerifyEmail #

<?php

interface MustVerifyEmail
{
    /**
     * Determine if the user has verified their email address.
     *
     * @return bool
     */
    public function hasVerifiedEmail();

    /**
     * Mark the given user's email as verified.
     *
     * @return bool
     */
    public function markEmailAsVerified();

    /**
     * Send the email verification notification.
     *
     * @return void
     */
    public function sendEmailVerificationNotification();

    /**
     * Get the email address that should be used for verification.
     *
     * @return string
     */
    public function getEmailForVerification();
}

参考父类示例 #

<?php

class User extends Model implements
    AuthenticatableContract,
    AuthorizableContract,
    CanResetPasswordContract
{
    use Authenticatable, Authorizable, CanResetPassword, MustVerifyEmail;
}

子类User #

<?php

use Illuminate\Contracts\Auth\MustVerifyEmail;
use Illuminate\Foundation\Auth\User as Authenticatable;

class User extends Authenticatable implements MustVerifyEmail
{
    /**
     * The attributes that are mass assignable.
     *
     * @var array<int, string>
     */
    protected $fillable = [
        'name',
        'email',
        'password',
    ];

    /**
     * The attributes that should be hidden for serialization.
     *
     * @var array<int, string>
     */
    protected $hidden = [
        'password',
    ];

    /**
     * The attributes that should be cast.
     *
     * @var array<string, string>
     */
    protected $casts = [
        'email_verified_at' => 'datetime',
        'password' => 'hashed',
    ];

    public function activeCode()
    {
        return //...
    }

    public function hasTwoFactor($key)
    {
        return //...
    }

    public function isTwoFactorAuthEnabled()
    {
        return //...
    }
}

这是因为Laravel提供了一个同名的Trait MustVerifyEmail，它已经实现了MustVerifyEmail接口中定义的所有方法。

你看到的User类继承的Authenticatable类，或者参考示例里的User类本身，已经引入了这个Trait。Trait中的方法会被自动注入到当前类中，相当于间接完成了接口的方法实现要求，所以不需要在User子类里重复编写这些方法。

具体细节：

• MustVerifyEmail Trait包含了接口要求的hasVerifiedEmail()、markEmailAsVerified()、sendEmailVerificationNotification()、getEmailForVerification()四个方法的完整实现
• 当User类继承Authenticatable时，如果父类已经引入该Trait，或者子类自己通过use关键字引入，这些方法就会成为User类的一部分
• PHP允许通过Trait来满足接口的实现要求，只要类或其继承链中的类引入的Trait覆盖了接口的所有方法，就无需手动重写

内容的提问来源于stack exchange，提问作者mahdi_sheykh