PHP array 的加法操作过程中的一个问题，大家可以继续往下看。

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

 
<?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); 
?> 


When executed, this script will print the following:
Union of $a and $b:

 
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。