toString()

只要将对象视为字符串，就会调用 __toString() 方法。此方法应返回类的字符串表示形式。

class User {
    public $first_name;
    public $last_name;
    public $age;

    public function __toString() {
        return "{$this->first_name} {$this->last_name} ($this->age)";
    }
}

$user = new User();
$user->first_name = "Chuck";
$user->last_name = "Norris";
$user->age = 76;

// Anytime the $user object is used in a string context, __toString() is called

echo $user; // prints 'Chuck Norris (76)'

// String value becomes: 'Selected user: Chuck Norris (76)'
$selected_user_string = sprintf("Selected user: %s", $user);

// Casting to string also calls __toString()
$user_as_string = (string) $user;