PHP foreach Array_merge problems and puzzles

Code:

$a = array('a' => array('a'));$b = array('b' => array('b'));foreach ($b as $key => &$item) {    $item[] = 'd';}$a = array_merge($b, $a);$b['b'][] = 'c';print_r($a);print_r($b);

Results:

Array(    [b] => Array        (            [0] => b            [1] => d            [2] => c        )    [a] => Array        (            [0] => a        ))Array(    [b] => Array        (            [0] => b            [1] => d            [2] => c        ))

My confusion is why after the merger, the operation on $b affects $ A.
Know the great God, please excuse me, thank you!

Reply content:

Code:

$a = array('a' => array('a'));$b = array('b' => array('b'));foreach ($b as $key => &$item) {    $item[] = 'd';}$a = array_merge($b, $a);$b['b'][] = 'c';print_r($a);print_r($b);

Results:

Array(    [b] => Array        (            [0] => b            [1] => d            [2] => c        )    [a] => Array        (            [0] => a        ))Array(    [b] => Array        (            [0] => b            [1] => d            [2] => c        ))

My confusion is why after the merger, the operation on $b affects $ A.
Know the great God, please excuse me, thank you!

Actually, I feel like you changed the Print_r into a var_dump, you can see it.

array (size=2)  'b' => &    array (size=3)      0 => string 'b' (length=1)      1 => string 'd' (length=1)      2 => string 'c' (length=1)  'a' =>     array (size=1)      0 => string 'a' (length=1)array (size=1)  'b' => &    array (size=3)      0 => string 'b' (length=1)      1 => string 'd' (length=1)      2 => string 'c' (length=1)

Variable b points to a reference type, so the value of B is changed, and the value of B in a changes with

Thank you for the sound of the Horn's reply, I again Google "php foreach reference", found this article, better understand the problem

A side question for a variable reference in the "PHP" Foreach Loop

I say I understand that when using the & symbol, the variable $b and the $item will point to an address at the same time, $b becomes a reference variable, if after foreach, unset drop $item, this time will be lifted $b reference.

