PHP中如何实现契约编程？

function divide($a, $b) {
    // 前置条件：检查除数不能为零
    if ($b == 0) {
        throw new InvalidArgumentException("除数不能为零");
    }

    // 执行除法操作
    $result = $a / $b;

    // 后置条件：检查结果是否为数字
    if (!is_numeric($result)) {
        throw new RuntimeException("除法结果不是数字");
    }

    return $result;
}

class Contract {
    public static function require($condition, $message) {
        if (!$condition) {
            throw new InvalidArgumentException($message);
        }
    }

    public static function ensure($condition, $message) {
        if (!$condition) {
            throw new RuntimeException($message);
        }
    }

    public static function invariant($condition, $message) {
        if (!$condition) {
            throw new LogicException($message);
        }
    }
}

function divide($a, $b) {
    Contract::require($b != 0, "除数不能为零");

    $result = $a / $b;

    Contract::ensure(is_numeric($result), "除法结果不是数字");

    return $result;
}

function contractDecorator($function) {
    return function (...$args) use ($function) {
        Contract::require(count($args) == 2, "需要两个参数");
        Contract::require(is_numeric($args[0]) && is_numeric($args[1]), "参数必须是数字");

        $result = $function(...$args);

        Contract::ensure(is_numeric($result), "结果必须是数字");

        return $result;
    };
}

$divideWithContract = contractDecorator(function($a, $b) {
    return $a / $b;
});

echo $divideWithContract(10, 2); // 输出: 5