从字符串的其余部分提取前导空格

I'm looking for the quickest approach to splitting a string into its leading spaces and the rest of it?

····sth should become array("····", "sth") and ·sth· - array("·", "sth·")

* · = space

$result = preg_split('/^(\s*)/', '  test ', -1, PREG_SPLIT_NO_EMPTY | PREG_SPLIT_DELIM_CAPTURE);

outputs

array(2) {
  [0]=>
  string(2) "  "
  [1]=>
  string(5) "test "
}

Here's a more simple approach:

$result = preg_split('/\b/', '   sth', 2);

Would output:

array (size=2)
  0 => string '   ' (length=3)
  1 => string 'sth' (length=3)