class Foobar
{
    public static function fromModelAttributes($attributes, $key, $model);

    public function toModelAttributes($attributes, $key, $model);
}

$user = User::create([
    'name' => 'Taylor',
    'token' => new Token('larav3l-secr3t')
]);

$user->update([
    'token' => new Token('adam123')
]);

// set object properties
$user->address->line1 = 'Infinite Loop 1';
$user->address->city = 'Cupertino';
$user->address->zip = '95014';
$user->address->region = 'CA';
$user->save();

// set entire object
$user->address = new Address('19111 Pruneridge Avenue', null, 'Cupertino', 'CA', '95014', null);
$user->save();

// unset an object
$user->address = null;
$user->save();
echo $user->address->line1; // null

$user->token = 'larav3l-secr3t';
$user->save();

$user->address->validate(); // bool

<?php

class User extends Model
{
    protected $guarded = [];

    protected $casts = [
        'address' => Address::class,
        'token' => Token::class,
        'meta' => Json::class,
    ];
}

<?php

class Token
{
    public $token;

    public function __construct($token)
    {
        $this->token = $token;
    }

    public static function fromModelAttributes($attributes, $key)
    {
        return new static(
            empty($attributes[$key]) ? null : decrypt($attributes[$key])
        );
    }

    public function toModelAttributes($attributes, $key)
    {
        return [
            $key => encrypt($this->token),
        ];
    }
}

<?php

class Address
{
    public $line1, $line2, $city, $region, $zip, $country;

    public function __construct(...$address)
    {
        [$this->line1, $this->line2, $this->city, $this->region, $this->zip, $this->country] = $address;
    }

    public function validate()
    {
        return Validator::make($this->toModelAttributes(), [
            'line1' => 'required',
            'city' => 'required',
            'zip' => 'required',
            'country' => 'required',
        ])->passes();
    }

    public static function fromModelAttributes($attributes, $key)
    {
        $address = array_map(function ($key) use ($attributes) {
            return $attributes[$key] ?? null;
        }, ['line1', 'price', 'city', 'region', 'zip', 'country']);

        return new static(...$address);
    }

    public function toModelAttributes()
    {
        return get_object_vars($this);
    }
}

<?php

namespace App;

class Json
{
    public $json;

    public function __construct($json = null)
    {
        $this->json = is_array($json) ? json_decode(json_encode($json)) : $json;
    }

    public static function fromModelAttributes($attributes, $key)
    {
        return new static(
            empty($attributes[$key]) ? null : json_decode($attributes[$key])
        );
    }

    public function toModelAttributes($attributes, $key)
    {
        return [
            $key => json_encode($this->json),
        ];
    }

    public function __get($name)
    {
        return $this->json->{$name};
    }

    public function __set($name, $value)
    {
        if (is_null($this->json)) {
            $this->json = (object) [];
        }

        if (is_array($value)) {
            $value = (object) $value;
        }

        $this->json->{$name} = $value;
    }
}