Singleton mode and factory mode in PHP

Concept of singleton pattern

The singleton pattern refers to a design pattern in which a class has only one object instance in the entire application.

Characteristics of the singleton pattern

A class has only one instance in the entire application

The class must create this instance by itself

You must provide this instance to the entire system by yourself

The reason for using the singleton mode in PHP

Most of my operations in PHP involve dealing with various databases, including mysql, redis, Memcache and other relational and non-relational databases, so there will be a large number of operations to connect to the database in an application. If the singleton mode is not used, new operations will be required every time, but each new will consume a lot of memory resources and system resources, and every time a database connection is opened and closed, it is a great test and waste of the database.

Need a static member variable that holds the only instance of the class (usually $instance is a private variable)

Constructors and clone functions must be declared private , in order to prevent the new class of external programs from losing the meaning of the singleton mode

A public static method must be provided to access this instance, thereby returning a reference to the only instance

//设计模式
//单例模式  都是使用同一个对象
//class Ren
//{
//    public $name;
//    private static $dx;   //存储对象
//
//    private function __construct()
//    {
//
//    }
//
//    public static function DuiXiang()
//    {
//        if(empty(self::$dx))
//        {
//            self:;$dx=new Ren();
//        }
//        return self::$dx;
//    }
//}
//
//$r= Ren::DuiXiang();

//把构造函数变为私有
//做了一个方法来间接造对象
//在该方法里面加限制

Factory class

refers to a class that contains a method specifically used to create other objects. The factory class is crucial in the practice of polymorphic programming, which allows dynamic replacement of classes. , modifying the configuration usually makes the application more flexible, and it is important for advanced PHP developers to be proficient in the factory mode.

The factory pattern is usually used to return different classes that conform to similar interfaces. A common use of factories is to create polymorphic providers, allowing us to decide which ones should be instantiated based on application logic or configuration settings. A class, for example, can be extended using such a provider to use the new extended name without the need to refactor other parts of the application.

Usually, the factory pattern has a key construct, which is a static method named Factory according to the general principle. However, this is just a principle. The factory method can be named arbitrarily. This static method can also accept parameters of any data. It must be Return an object.

class YunSuan
{
    public $a;
    public $b;
    function Suan()
    {
        echo "对两个数进行运算";
    }

class gongchang
{   //功能 ： 给一个参数，返回一个对象
    static function chanpin($name)
    {
        switch($name)
        {
            case "'+":
                return new jia();
                break;
            case "-";
                return new jian();
                break;
        }
    }
}

$a=gongchang::chanpin("+");

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