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The + operator appends elements of remaining keys from the right handed array to the left handed, whereas duplicated keys are NOT overwritten.

今天 再次看 php manual的时候，才知道
复制代码 代码如下:
<?php
$a = array("a" => "apple", "b" => "banana");
$b = array("a" => "pear", "b" => "strawberry", "c" => "cherry");
$c = $a + $b; // Union of $a and $b
echo "Union of \$a and \$b: \n";
var_dump($c);
$c = $b + $a; // Union of $b and $a
echo "Union of \$b and \$a: \n";
var_dump($c);
?>

"codetitle">复制代码 代码如下:
array(3) {
["a"]=>
string(5) "apple"
["b"]=>
string(6) "banana"
["c"]=>
string(6) "cherry"
}
Union of $b and $a:
array(3) {
["a"]=>
string(4) "pear"
["b"]=>
string(10) "strawberry"
["c"]=>
string(6) "cherry"
}

原来，我的理解就是。直接把$b中的元素直接复制到$a中。
我错了。