obj.php

<?php
function obj( $json_str = null ) {
  $obj = new stdClass();
  $json = json_decode( $json_str );
  if ( $json !== null ) {
    foreach( $json as $k => $v ) {
      $obj->{"{$k}"} = $v;
    }
  }
  return $obj;
}

//--------------------

$obj1 = obj();
$obj2 = obj('{
  "name"  : "ムグお",
  "id"    : "mgng",
  "sites" : [
    "https://twitter.com/mgng",
    "http://mgngoccult.tumblr.com/"
  ]
}');

print_r( $obj1 );
print_r( $obj2 );

obj_result.txt

stdClass Object
(
)
stdClass Object
(
    [name] => ムグお
    [id] => mgng
    [sites] => Array
        (
            [0] => https://twitter.com/mgng
            [1] => http://mgngoccult.tumblr.com/
        )

)