警告：从空价值创建默认对象，在PHP 8中，我会收到关键的未接收错误：尝试分配属性“长度”在null上

Question

WordPress 5.9.2 和 WooCommerce 6.3.1 使用此代码：

public function calculate_shipping( $package = array() ) {

    global $woocommerce;

    $address['suburb']   = $package['destination']['city'];
    $address['state']    = $package['destination']['state'];
    $address['postcode'] = $package['destination']['postcode'];
    $address['country']  = $package['destination']['country'];

    $i           = 0;
    $totalweight = 0;
    $totalprice  = 0;

    foreach ( $woocommerce->cart->get_cart() as $item_id => $values ) {
        $_product = $values['data'];
        $q        = 1;
        while ( $values['quantity'] >= $q ) {
            $products[ $i ]->length = $_product->length;
            $products[ $i ]->height = $_product->height;
            $products[ $i ]->width  = $_product->width;
            $products[ $i ]->weight = $_product->weight;
            $totalweight           += $_product->weight;
            $totalprice            += $_product->get_price();
            $q++;
            $i++;
        }
    }
}

与长度、高度、宽度和重量相关：
$products[$i]->length = $_product->length;

Answer 1

首先，让我们创建一个可以更容易测试的独立示例：

class Example {
    public $length, $height, $width, $weight;
    
    public function __construct($length, $height, $width, $weight) {
        $this->length = $length;
        $this->height = $height;
        $this->width = $width;
        $this->weight = $weight;
    }
    
    public function get_price() {
        return 1.23;
    }
}

$sample_data = [
    42 => ['quantity' => 2, 'data' => new Example(42, 42, 42, 42)],
    69 => ['quantity' => 1, 'data' => new Example(69, 69, 69, 69)],
];

$i           = 0;
$totalweight = 0;
$totalprice  = 0;

foreach ( $sample_data as $item_id => $values ) {
    $_product = $values['data'];
    $q        = 1;
    while ( $values['quantity'] >= $q ) {
        $products[ $i ]->length = $_product->length;
        $products[ $i ]->height = $_product->height;
        $products[ $i ]->width  = $_product->width;
        $products[ $i ]->weight = $_product->weight;
        $totalweight           += $_product->weight;
        $totalprice            += $_product->get_price();
        $q++;
        $i++;
    }
}

var_dump($products);

现在我们可以看到这在旧版本的PHP上做了什么，例如使用此方便的工具，该工具在多个版本上运行相同的代码。

php 7.4中的输出是这样：

Warning: Creating default object from empty value in /in/1Imu2 on line 31

Warning: Creating default object from empty value in /in/1Imu2 on line 31

Warning: Creating default object from empty value in /in/1Imu2 on line 31
array(3) {
  [0]=>
  object(stdClass)#3 (4) {
    ["length"]=>
    int(42)
    ["height"]=>
    int(42)
    ["width"]=>
    int(42)
    ["weight"]=>
    int(42)
  }
  [1]=>
  object(stdClass)#4 (4) {
    ["length"]=>
    int(42)
    ["height"]=>
    int(42)
    ["width"]=>
    int(42)
    ["weight"]=>
    int(42)
  }
  [2]=>
  object(stdClass)#5 (4) {
    ["length"]=>
    int(69)
    ["height"]=>
    int(69)
    ["width"]=>
    int(69)
    ["weight"]=>
    int(69)
  }
}

因此，我们可以看到正在发生的事情是，对于每个项目，代码在分配其上的属性之前隐含地创建stdclass对象。因此，修复程序是为了通过编写$ products [$ i] = new STDCLASS;在$ products [$ i] - ＆gt; lentht = $ _Product- ;在我们使用时，我们还应该创建$ propertys作为一个空数组，$ products = []; foreach < foreach < /代码>循环。

在同一工具中运行我们的修改代码我们现在可以看到它现在从php的每个PHP版本中给出了相同的结果5.4直至8.1，没有警告。