What is PHP singleton mode?

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In fact, a singleton pattern, plainly speaking, is that a class can only be instantiated once. But how do we make a fuss at this instantiation? In fact, there is a breakthrough is __construct () this magic method. This method means that the method is automatically executed if the class is instantiated. And if I turn this method into a protection or a private one, what would it be?

static function getInstance($class, $param = array()){    if (!isset($obj[$class])) {        $obj[$class] = new $class($param);    }    return $obj[$class];}在实例化一个类时，先判断是否有这个类的实例，如果有就不实例化，反之就实例化一个

Strong landlord is cheap,show to talk about is that you my code.

The simplest class of PHP singleton patterns:

class TestInstance{    public static $_instance = null;    //为了防止外部new这个类，所以构造方法用protected，这是单例模式的关键之处    protected function __Construct()    {        echo 'Instance,Instance,Instance..........';    }    //用一个静态变量存储类的实例，只有第一次实例化的时候才赋值，以后都直接给出静态实例    public static function getInstance()    {        if(!isset(self::$_instance)){            self::$_instance = new static();        }        return self::$_instance;    }}

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