数组加操作将所有数组视为关联数组。 当加号期间键冲突时，左边(上一个)值将被保留

我在下面发布代码以使事情更清楚。

$a + $b = array_plus($a， $b)

function array_plus($a, $b){
    $results = array();
    foreach($a as $k=>$v) if(!isset($results[$k]))$results[$k] = $v;
    foreach($b as $k=>$v) if(!isset($results[$k]))$results[$k] = $v;
    return $results;
}

引用自PHP语言操作符手册

+操作符返回右数组附加到左数组;对于两个数组中都存在的键，将使用左边数组中的元素，而忽略右边数组中的匹配元素。

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+的逻辑等价于下面的代码片段:

$union = $array1;

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

如果您对c级实现的细节感兴趣，请转到

php-src / Zend / zend_operators.c

注意，+与array_merge()组合数组的方式不同:

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

会给你

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
)

更多示例请参见链接页面。

小心使用数字键，如果它们应该保留，或者如果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
)

走

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

从https://softonsofa.com/php-array_merge-vs-array_replace-vs-plus-aka-union/

也就是说，我们可以认为+运算符有点多余，因为array_replace函数也可以实现同样的效果。 然而，在有些情况下，它派上用场:假设你有一个$options数组被传递给一个函数/方法，也有默认值用作备用:

// we could do it like this
function foo(array $options)
{
   $defaults = ['foo' => 'bar'];
   
   $options = array_replace($defaults, $options);
 
   // ...
}
 
// but + here might be way better:
function foo(array $options)
{
   $options += ['foo' => 'bar'];
 
   // ...
}

$var1 = "example";
$var2 = "test";
$output = array_merge((array)$var1,(array)$var2);
print_r($output);

数组([0]=> example [1] => test)

+操作符产生的结果与array_replace()相同。但是，由于运算符参数颠倒了，结果数组的顺序也可能不同。

从本页展开另一个例子:

$array1 = array('one', 'two', 'foo' => 'bar');
$array2 = array('three', 'four', 'five', 'foo' => 'baz'); 

print_r($array1 + $array2);
print_r(array_replace($array2, $array1)); //note reversed argument order

输出:

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