PHP This self usage and differences

This self

$this refers to an instantiated object, and self refers to the current class

     $db   = new imooc\database () var_dump ($db->where (' id=1 '));D The atabase  class returns the $this,  print to see that $this is an instantiated object of the Database class. Now look at self this keyword class database{     private static  $db;     static function getinstance ()      {        if  (self:: $db)  {             return self:: $db;         } else {             self:: $db  = new self ();             return self:: $db;         }    }} or database This class &nbsp, defined static private variable (only class to call), because $this is pointing to the object so with the $this->db will be error, self point to the database of the class itself, I () The equivalent of instantiating the object of the database class.

PHP This self usage and differences