# 对称阵列解构

**官方解释：**短数组语法（*\[]*）现在可以用于将数组的值赋给一些变量（包括在*foreach*中）。 这种方式使从数组中提取值变得更为容易。

以下是官方示例：**但是经过我测试（PHP Version 7.1.5），是一个错误的例子**

```php
<?php
$data = [
    ['id' => 1, 'name' => 'Tom'],
    ['id' => 2, 'name' => 'Fred'],
];

while (['id' => $id, 'name' => $name] = $data) {
    // logic here with $id and $name
}
```

我们知道在 PHP5.4 之前只能通过 `array()` 来定义数组，5.4之后添加了 `[]` 的简化写法（省略了5个字符还是很实在的）。

```php
<?php
// 5.4 之前
$array = array(1, 2, 3);
$array = array("a" => 1, "b" => 2, "c" => 3);

// 5.4 及之后
$array = [1, 2, 3];
$array = ["a" => 1, "b" => 2, "c" => 3];
```

引申到另外一个问题上，如果我们要把数组的值赋值给不同的变量，可以通过 `list` 来实现：

```php
<?php
list($a, $b, $c) = $array;

list($a,$b)=array(10,20);
echo $a,'~',$b,'<br />';
//返回10~20

list($a,$b,,$c)=array(2=>10,3=>20,4=>30,1=>40);
echo $a,'~',$b,'~',$c,'<br />';
//返回notice~40~20
//执行到$a的时候返回给我一个notice：说数组没有0键
```

为什么会返回这个notice\~40\~20呢？ [查看解释](http://www.cnblogs.com/ggbd-lie/p/3269192.html)

PHP7.1 实现了一下特性。但是要注意的是：出现在左值中的 `[]` 并不是数组的简写，是 `list()` 的简写。

但是并不仅仅如此，新的 `list()` 的实现并不仅仅可以出现在左值中，也能在 `foreach` 循环中使用：

```php
$data = [
    ['id' => 1, 'name' => 'Tom'],
    ['id' => 2, 'name' => 'Fred'],
];


foreach ($data as ['id' => $id, 'name' => $name]) {
    echo $id . PHP_EOL;
    echo $name. PHP_EOL;
}
```

结果：

```
id:1 name:Tom id:2 name:Fred
```

不过因为实现的问题，`list()`和`[]`不能相互嵌套使用：


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