Implementation of php singleton pattern_PHP tutorial

<?<span php

</span><span /*</span><span *
* 设计模式之单例模式
* $_instance必须声明为静态的私有变量
* 构造函数和析构函数必须声明为私有,防止外部程序new
* 类从而失去单例模式的意义
* getInstance()方法必须设置为公有的,必须调用此方法
* 以返回实例的一个引用
* ::操作符只能访问静态变量和静态函数
* new对象都会消耗内存
* 使用场景:最常用的地方是数据库连接。 
* 使用单例模式生成一个对象后，
* 该对象可以被其它众多对象所使用。 
</span><span */</span>
<span class</span><span  Example
{
</span><span //</span><span 保存例实例在此属性中</span>
<span private</span> <span static</span> <span $_instance</span><span ;

</span><span //</span><span 构造函数声明为private,防止直接创建对象</span>
<span private</span> <span function</span><span  __construct()
{
</span><span echo</span> 'I am Construceted'<span ;
}

</span><span //</span><span 单例方法</span>
<span public</span> <span static</span> <span function</span><span  singleton()
{
</span><span if</span>(!<span isset</span>(self::<span $_instance</span><span ))
{
</span><span $c</span>=<span __CLASS__</span><span ;
self</span>::<span $_instance</span>=<span new</span> <span $c</span><span ;
}
</span><span return</span> self::<span $_instance</span><span ;
} 

</span><span //</span><span 阻止用户复制对象实例</span>
<span public</span> <span function</span><span  __clone()
{
</span><span trigger_error</span>('Clone is not allow' ,<span E_USER_ERROR</span><span );
}

</span><span function</span><span  test()
{
</span><span echo</span>("test"<span );

}
}

</span><span //</span><span  这个写法会出错，因为构造方法被声明为private</span>
<span $test</span> = <span new</span><span  Example;

</span><span //</span><span  下面将得到Example类的单例对象</span>
<span $test</span> = Example::<span singleton();
</span><span $test</span>-><span test();

</span><span //</span><span  复制对象将导致一个E_USER_ERROR.</span>
<span $test_clone</span> = <span clone</span> <span $test</span><span ;
</span>?>

First of all, we need to understand the concept of singleton mode. So what is singleton mode?

The singleton mode, as the name suggests, means that there is only one instance.

As an object creation mode, the singleton mode ensures that a class has only one instance, instantiates itself and provides this instance to the entire system,

We call this class a singleton class.

There are three main points of the singleton pattern:

Let’s discuss why we should use PHP singleton mode?

Most people understand the use of the singleton pattern literally, thinking that it saves system resources, avoids repeated instantiation, and is a kind of "family planning". And PHP Every time the page is executed, all resources will be cleared from the memory. Therefore, the singleton in PHP actually needs to be re-instantiated every time it is run, thus losing the meaning of repeated instantiation of the singleton. Just start from In this respect, PHP's singleton is indeed a bit disappointing. But does a singleton only have this function and application? The answer is no, let's take a look.

1. PHP is mainly used in database applications, so there will be a large number of database operations in an application. When developing in an object-oriented way (nonsense), if you use the singleton mode, you can avoid a large number of operations. The resources consumed by the new operation.

2. If a class is needed to globally control certain configuration information in the system, it can be easily implemented using the singleton mode. This can be found in the FrontController part of zend Framework.

3. In a page request, it is easy to debug because all the code (such as database operation class db) is concentrated in one class. We can set hooks in the class and output logs to avoid going everywhere. var_dump, echo.