What is php singleton pattern?

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In fact, the singleton model, to put it bluntly, means that a class can only be instantiated once. But how do we make a fuss about this instantiation? In fact, a breakthrough is the magic method __construct(). This method means that if the class is instantiated, this method will be automatically executed. Then if I make this method protected or private, what will be the effect?

<code class="language-text"><?php
class test{

	protected function __construct(){

	}
}

$test = new test();
?>
</code>

<code class="language-php"><span class="x">static function getInstance($class, $param = array())</span>
<span class="x">{</span>
<span class="x">    if (!isset($obj[$class])) {</span>
<span class="x">        $obj[$class] = new $class($param);</span>
<span class="x">    }</span>
<span class="x">    return $obj[$class];</span>
<span class="x">}</span>
<span class="x">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</span>
</code>

Awesome, the host is invincible Talk is cheap,show you my code.

The simplest PHP singleton mode class:

<code class="language-php"><span class="x">class TestInstance</span>
<span class="x">{</span>
<span class="x">    public static $_instance = null;</span>

<span class="x">    //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</span>
<span class="x">    protected function __Construct()</span>
<span class="x">    {</span>
<span class="x">        echo 'Instance,Instance,Instance..........';</span>
<span class="x">    }</span>

<span class="x">    //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</span>
<span class="x">    public static function getInstance()</span>
<span class="x">    {</span>
<span class="x">        if(!isset(self::$_instance)){</span>
<span class="x">            self::$_instance = new static();</span>
<span class="x">        }</span>

<span class="x">        return self::$_instance;</span>
<span class="x">    }</span>
<span class="x">}</span>
</code>