PHP foreach 循环中变量意外持久化问题及解决方案

foreach ($study->children() as $rawPart) {
   $isAnnex = $rawPart->template()->name() === 'annex';

   $preparedPart; // 关键问题所在
   $preparedPart['title'] = (string)$rawPart->title();
   $preparedPart['type'] = (string)$rawPart->template()->name();
   // …etc.

   if ($isAnnex) {
      $preparedPart['title2'] = (string)$rawPart->title();
   }
   // 假设这里会将 $preparedPart 添加到一个结果数组中
   // 例如：$results[] = $preparedPart;
}

{
  "parts": [
    { "title": "Edito de Christo…", "type": "annex", "title2": "Edito de Christo…" },
    { "title": "Introduction", "type": "annex", "title2": "Introduction" },
    { "title": "M\u00e9thodologie", "type": "annex", "title2": "M\u00e9thodologie" },
    { "title": "Le projet et l'organisation", "type": "part", "title2": "M\u00e9thodologie" }, // 错误：title2 继承了上一个 annex 的值
    { "title": "L\u2019adresse aux publics", "type": "part", "title2": "M\u00e9thodologie" }  // 错误：title2 继承了上一个 annex 的值
  ]
}

foreach ($study->children() as $rawPart) {
   $isAnnex = $rawPart->template()->name() === 'annex';

   $preparedPart = []; // 正确：每次迭代都将 $preparedPart 初始化为空数组
   $preparedPart['title'] = (string)$rawPart->title();
   $preparedPart['type'] = (string)$rawPart->template()->name();
   // …etc.

   if ($isAnnex) {
      $preparedPart['title2'] = (string)$rawPart->title();
   }
   // 假设这里会将 $preparedPart 添加到一个结果数组中
   // 例如：$results[] = $preparedPart;
}

echo "--- 错误示例 (变量未正确初始化) ---\n";
$b = null; // 模拟循环外或第一次迭代前的状态
foreach ( [1,2,3,4] as $number ) {
   $a = null; // 正确：每次迭代都清空 $a
   $b;        // 错误：此行不做任何事， $b 会保留其值

   if ( $number % 2 === 1 ) { // 如果是奇数
      $a = $number;
      $b = $number;
   }
   var_dump("Number: $number", "a: $a", "b: $b");
}
/*
输出结果：
--- 错误示例 (变量未正确初始化) ---
string(10) "Number: 1"
string(4) "a: 1"
string(4) "b: 1"
string(10) "Number: 2"
string(4) "a: "   // $a 被重置为 null
string(4) "b: 1"   // $b 保持了上一次迭代的值
string(10) "Number: 3"
string(4) "a: 3"
string(4) "b: 3"
string(10) "Number: 4"
string(4) "a: "
string(4) "b: 3"   // $b 保持了上一次迭代的值
*/

echo "\n--- 正确示例 (变量每次迭代都初始化) ---\n";
foreach ( [1,2,3,4] as $number ) {
   $a = null; // 每次迭代都清空 $a
   $b = null; // 正确：每次迭代都清空 $b

   if ( $number % 2 === 1 ) { // 如果是奇数
      $a = $number;
      $b = $number;
   }
   var_dump("Number: $number", "a: $a", "b: $b");
}
/*
输出结果：
--- 正确示例 (变量每次迭代都初始化) ---
string(10) "Number: 1"
string(4) "a: 1"
string(4) "b: 1"
string(10) "Number: 2"
string(4) "a: "
string(4) "b: "   // $b 被正确重置为 null
string(10) "Number: 3"
string(4) "a: 3"
string(4) "b: 3"
string(10) "Number: 4"
string(4) "a: "
string(4) "b: "   // $b 被正确重置为 null
*/