php函数调用中的下划线

Question

I know that underscores in function names in PHP is used to "implicitly" denote that they are supposed to be private...but I just saw this code:

class DatabaseConnection
{
  public static function get()
  {
    static $db = null;
    if ( $db == null )
      $db = new DatabaseConnection();
    return $db;
  }

  private $_handle = null;

  private function __construct()
  {
    $dsn = 'mysql://root:password@localhost/photos';
    $this->_handle =& DB::Connect( $dsn, array() );
  }

  public function handle()
  {
    return $this->_handle;
  }
}

print( "Handle = ".DatabaseConnection::get()->handle()."
" );
print( "Handle = ".DatabaseConnection::get()->handle()."
" );

in this code, what does it mean to have underscores in variables?

Answer 1

It's kind of the same for methods and properties : the convention is the same : having a name that starts by one underscore generally means they are to be considered as private/protected.

(Of course, it's not the same with methods which have a name that starts by two underscore : those are magic methods, and two underscore should not be used for your "normal" method names)