array_change_key_case 底层代码

function convert_to_key_case($data, $case){

         $condition = ($case == 'lowercase')? 'lowercase' : 'uppercase';
         $test = [];
         foreach($data as  $key => $value) {
             if ($condition == 'lowercase') {
                 $test[strtolower($key)] = $value;
             } else {
                 $test[strtoupper($key)] = $value;
             }
         }
     return $test;
 }

 $input = ['test1'=>1, 'Test2' => 2, 'TeSt3' => 3];

 print_r(convert_to_key_case($input, 'uppercase'));
 print_r(convert_to_key_case($input, 'lowercase'));

 OUTPUT

 Array 
 (
  [TEST1] => 1
  [TEST2] => 2 
  [TEST3] => 3 
 )

 Array ( 
  [test1] => 1
  [test2] => 2
  [test3] => 3
  )