合并php数组时如何保留键名

$array1 = ['a' => 'apple', 'b' => 'banana'];
$array2 = ['c' => 'cherry', 'd' => 'date'];

$mergedArray = $array1 + $array2;

[
  'a' => 'apple',
  'b' => 'banana',
  'c' => 'cherry',
  'd' => 'date'
]