Programmer-PHP Custom function before adding &, why the effect is the same, on all the code

$a = ' wap ';
$b = ' KKK ';

function sum($p){     return $p.='aaa';}function &sum2($p){    return $p.='bbb';} echo sum($a); echo "
"; echo sum2($b);

Reply content:

$a = ' wap ';
$b = ' KKK ';

function sum($p){     return $p.='aaa';}function &sum2($p){    return $p.='bbb';} echo sum($a); echo "
"; echo sum2($b);

I have answered your question in one of your other questions, in this case, if you want to compare, you can modify the code to:

$a = 'wap';$b ='kkk';function sum($p){     return $p.='aaa';}function &sum2(&$p){    return $p.='bbb';}//既然是返回引用，自然不能使用形参传递，所以将$p改为&$p echo sum($a);//output is wapaaa echo "
"; echo sum2($b);//output is kkkbbb echo "
"; echo sum($a);//output is wapaaa echo "
"; echo sum2($b);//output is kkkbbbbbb

