为什么有一个"&"($ arr as&$ value)？

Question

$arr = array(1, 2, 3, 4);
foreach ($arr as &$value) {
    $value = $value * 2;
}

foreach (array_expression as $value)
    statement
foreach (array_expression as $key => $value)
    statement

$ key是否意味着数组的索引？

Answer 1

&$variable_name 是PHP通过引用传递的方式:

请参阅:http://php.net/manual/en/language.references.pass.php

有关参考资料的更多解释,请参阅:http: //www.php.net/manual/en/language.references.whatare.php

Answer 2

    $arr = array(1, 2, 3, 4);

    foreach ($arr as $value)
       $value = $value * 100;
    echo implode(' ', $arr); // 1 2 3 4

    foreach ($arr as &$value)
        $value = $value * 100;
    echo implode(' ', $arr); // 100 200 300 400

得到它了？