PHP 数组操作使用 "+" 与 array_merge要注意的一些细节问题

<?php
   $a = ['a','b'];
   $b = ['c','d','e'];
   $c = $a + $b;  //['a','b','e']
?>

<?php
   //e.g.1
   $a = ['a','b'];
   $b = ['c','d','e'];
   $c = array_merge($a , $b);//['a','b','c','d','e']
   
   //e.g.2
    $a = ['a'=> 1,'b'=> 4];
    $b = ['a' => 2,'d'=> 6];
    $c = array_merge($a , $b);//["a" => 2,"b" => 4,"d" => 6]
?>