实例探索PHP只读属性改变游戏规则的特性

class UserProfile {
    public readonly string $username;
    public function __construct(string $username) {
        $this->username = $username;
    }
}

phpCopy codeclass UserProfile {
    public readonly string $username;public readonly string $username;
    public readonly ?string $bio;
    public function __construct(string $username, ?string $bio = null) {
        $this->username = $username;
        $this->bio = $bio;
    }
}

class ImmutableDate {
    public readonly DateTimeImmutable $date;
    public function __construct(DateTimeImmutable $date) {
        $this->date = $date;
    }
}

class Circle {
    public readonly float $radius;
    public readonly float $area;

    public function __construct(float $radius) {
        $this->radius = $radius;
        $this->area = $this->calculateArea();
    }
    private function calculateArea(): float {
        return pi() * $this->radius * $this->radius;
    }
}

class MyClass {
    public readonly string $immutableProperty;
    public function __construct(string $value) {
        $this->immutableProperty = $value;
    }
    public function getImmutableProperty(): string {
        return $this->immutableProperty;
    }
    public function setImmutableProperty(string $newValue): void {
        $this->immutableProperty = $newValue;
    }
}