if(ref_type(($ref_type eq 'HASH')? $ref->{$key}: $ref->[$key]))
{ return "Can't replace Reference by Value in ".join('_',@path)." ($key)"; }

sub QueryToHash
{
  my $query = shift ;           # der string mit der Query
  my $result;
  $result={};

  for my $parameter (split(/\&/, $query))
  {
    my ( $p_name, $p_value ) = split(/=/, $parameter,2);
    my $error=set_value($result,[split(/_/,$p_name)],$p_value);
    warn $error if($error);
  }

  return $result;
}

sub set_value
{
  my $ref=shift;
  my $res=\$ref;
  my $query=shift;
  my $val=shift;

  my @path;
  for my $key ( @$query )
  {
    push(@path,$key);
    if ( $key=~/^\d+$/ )
    {
      if(ref($$res) && ref($$res) ne 'ARRAY')
      { return "Incorrect query! last key of '".join('_',@path)."' not same type as in tree\n"; }
      $res = \$$res->[$key];
    }
    else
    {
      if(ref($$res) && ref($$res) ne 'HASH')
      { return "Incorrect query! last key of '".join('_',@path)."' not same type as in refernce\n"; }
      $res = \$$res->{$key};
    }
  }

  if ( ref $$res )
  { return "Incorrect query! '".join('_',@path)."' points to a location that already holds data.\n"; }
  else
  { $$res = $val; }

  return 0;
}