Single-Case mode

/**
* Design pattern of a single case mode
* $_instance must be declared as a static private variable
* Constructors must be declared private to prevent the external program new class from losing the meaning of a singleton pattern
* The getinstance () method must be set to public, and this method must be called to return a reference to the instance
*:: operator can only access static variables and static functions
* New objects will consume memory
* Usage Scenario: The most common place is the database connection.
* Once an object is generated using singleton mode, the object can be used by many other objects.
*/
Class Mans
{
Save example instance in this property
private static $_instance;

The constructor is declared private, preventing the object from being created directly
Private Function __construct ()
{
Echo ' I was instantiated! ‘;
}

Single Case method
public static function Get_instance ()
{
Var_dump (Isset (self::$_instance));

if (!isset (self::$_instance))
{
Self::$_instance=new self ();
}
return self::$_instance;
}

Prevent users from replicating object instances
Private Function __clone ()
{
Trigger_error (' Clone is not allow ', e_user_error);
}

function test ()
{
Echo ("Test");

}
}

This is an error because the constructor method is declared as private.
$test = new Man;

The following will get the singleton object of the example class
$test = Man::get_instance ();
$test = Man::get_instance ();
$test->test ();

Copying an object will result in a e_user_error.
$test _clone = Clone $test;

Single-Case mode