PHP中的数组+运算符？

Question

$test = array('hi');
$test += array('test','oh');
var_dump($test);

+PHP中的数组意味着什么？

Answer 1

引用PHP语言操作员手册

+运算符返回附加到左侧数组的右侧数组; 对于存在于两个数组中的键,将使用左侧数组中的元素,并且将忽略右侧数组中的匹配元素.

所以,如果你这样做

$array1 = ['one',   'two',          'foo' => 'bar'];
$array2 = ['three', 'four', 'five', 'foo' => 'baz']; 

print_r($array1 + $array2);

你会得到

Array
(
    [0] => one   // preserved from $array1 (left-hand array)
    [1] => two   // preserved from $array1 (left-hand array)
    [foo] => bar // preserved from $array1 (left-hand array)
    [2] => five  // added from $array2 (right-hand array)
)

所以逻辑+相当于以下片段:

$union = $array1;

foreach ($array2 as $key => $value) {
    if (false === array_key_exists($key, $union)) {
        $union[$key] = $value;
    }
}

如果您对C级实现的详细信息感兴趣

• php-src/Zend/zend_operators.c

注意,这+与array_merge()组合数组的方式不同:

print_r(array_merge($array1, $array2));

会给你的

Array
(
    [0] => one   // preserved from $array1
    [1] => two   // preserved from $array1
    [foo] => baz // overwritten from $array2
    [2] => three // appended from $array2
    [3] => four  // appended from $array2
    [4] => five  // appended from $array2
)

有关更多示例,请参见链接页面

Answer 2

我发现使用它的最好例子是配置数组.

$user_vars = array("username"=>"John Doe");
$default_vars = array("username"=>"Unknown", "email"=>"no-reply@domain.com");

$config = $user_vars + $default_vars;

的$default_vars,因为它表明,为默认值的数组.该$user_vars数组将覆盖中定义的值$default_vars.任何缺失的值$user_vars现在都是默认值$default_vars.

这将print_r如下:

Array(2){
    "username" => "John Doe",
    "email" => "no-reply@domain.com"
}

我希望这有帮助!

Answer 3

此运算符采用两个数组的并集(与array_merge相同,但array_merge重复键被覆盖除外).

数组运算符的文档可在此处找到.

Answer 4

小心使用数字键,如果它们应该被保留或者你不想丢失任何东西

$a = array(2 => "a2", 4 => "a4", 5 => "a5");
$b = array(1 => "b1", 3 => "b3", 4 => "b4");

联盟

print_r($a+$b);
Array
(
    [2] => a2
    [4] => a4
    [5] => a5
    [1] => b1
    [3] => b3
)

合并

print_r(array_merge($a, $b));
Array
(
    [0] => a2
    [1] => a4
    [2] => a5
    [3] => b1
    [4] => b3
    [5] => b4
)