json大括号保存对象，为什么关联数组在json中表现为对象，用{}包裹关联数组的数据？

//关联数组

$result_array1['msg'] = 13;

$result_array1['infor'] = 24;

//索引数组

$result_array2[] = 1;

$result_array2[] = 2;

//索引数组

$arr = array(0,1,3);

$arr[0] = $result_array1;

$arr[1] = $result_array2;

$arr[2] = $result_array1;

$arr[3] = 123;

$arr[4] = 3243;



$result_array['msg'] = 13;

$result_array['infor'] = 24;

$result_array['ra1'] = $arr;



var_dump($result_array);

var_dump(json_encode($result_array));

 array (size=3)

  'msg' => int 13

  'infor' => int 24

  'ra1' =>

    array (size=5)

      0 =>

        array (size=2)

          'msg' => int 13

          'infor' => int 24

      1 =>

        array (size=2)

          0 => int 1

          1 => int 2

      2 =>

        array (size=2)

          'msg' => int 13

          'infor' => int 24

      3 => int 123

      4 => int 3243

string '{"msg":13,"infor":24,"ra1":[{"msg":13,"infor":24},[1,2],{"msg":13,"infor":24},123,3243]}' (length=88)

//关联数组

$result_array1['msg'] = 13;

$result_array1['infor'] = 24;

//索引数组

$result_array2[] = 1;

$result_array2[] = 2;

//索引数组

$arr = array(0,1,3);

$arr[0] = $result_array1;

$arr[1] = $result_array2;

$arr[2] = $result_array1;

$arr[3] = 123;

$arr[4] = 3243;



$result_array[] = 13;

$result_array[] = 24;

$result_array[] = $arr;



var_dump($result_array);

var_dump(json_encode($result_array));

array (size=3)

  0 => int 13

  1 => int 24

  2 =>

    array (size=5)

      0 =>

        array (size=2)

          'msg' => int 13

          'infor' => int 24

      1 =>

        array (size=2)

          0 => int 1

          1 => int 2

      2 =>

        array (size=2)

          'msg' => int 13

          'infor' => int 24

      3 => int 123

      4 => int 3243

D:\wamp\www\test\array.php:47:string '[13,24,[{"msg":13,"infor":24},[1,2],{"msg":13,"infor":24},123,3243]]' (length=68)

这个不是和json定义违背了吗?：

难道关联数组在PHP中是对象，而索引数组就不是对象，那它们的区别是什么????