Role.php

<?php

namespace My\Role;

use RoleId as BaseId;

class RoleId extends BaseId
{
    const ADMIN = 'Admin';
    const GUEST = 'Guest';
    
    protected static $validNames = [
        self::ADMIN,
        self::GUEST
    ];
    
    public function isAdmin()
    {
        return $this->name == static::ADMIN;
    }
    
    public function isGuest()
    {
        return $this->name == static::GUEST;
    }
}

class AdminRole extends AbstractRole
{
    public function roleId()
    {
        return RoleId::Admin();
    }
}

class GuestRole extends AbstractRole
{
    public function roleId()
    {
        return RoleId::Guest();
    }
}

abstract class AbstractRole implements RoleInterface
{
    protected $permissions = [];
    
    public function __construct(array $permissions)
    {
        $this->setPermissions($permissions);
    }
    
    public function isPermitted(Permission $permission)
    {
        return in_array($permission, $this->permissions);
    }
    
    private function addPermission(Permission $permission)
    {
        if (!$this->isPermitted($permission) {
            $this->permissions[] = $permission;
        }
    }
    
    private function setPermissions(array $permissions)
    {
        foreach ($permissions as $permission) {
            $this->addPermission($permission);
        }
    }
}

RoleId.php

<?php

class RoleId
{
    protected static $validNames = [];
    protected $name;
    
    public function __construct($name)
    {
        $this->name = trim($name);
        if (!empty(static::$validNames) && !in_array($this->name, static::$validNames)) {
            throw new DomainException("Invalid name [$name]");
        }
    }
    
    public static function __callStatic($name, array $arguments [])
    {
        return new static($name);
    }
    
    public function equals(self $other)
    {
        return $this->name == $other->name;
    }
    
    public function name()
    {
        return $this->name;
    }
    
    public function __toString()
    {
        return $this->name();
    }
}