An article to talk about DI dependency injection in php

What is DI dependency injection? The following article will give you an in-depth understanding of DI dependency injection in php. I hope it will be helpful to you!

What is DI/Dependency Injection

• Dependency Injection DI In fact, it essentially means Dependence on the class is completed through the constructorAutomatic injection
• In layman's terms, it means that you are currently operating a class, but some methods or functions of this class cannot be achieved by relying on this class alone. It can be completed only with the help of another class
The most direct sign is when the parameter data is passed as an object. Strictly speaking, you
• want to operate one class in another class. There is an interdependence relationship between the two classes. The method of passing parameters is called injection

The reason why dependency injection appears

When dependency injection is not used,
• php When you need to use another class in one class , often the following operations are performed
For example, if I need to use the
• adapter class in the container class, I need to instantiate it before use
If a large number of external classes need to be used, this will cause
• the degree of coupling to be too high, which can easily lead to later maintenance difficulties
In lay terms, That is,
• container cannot work without external classes. This is called too high coupling

<?php
class container
{
    private $adapter;

    public function __construct()
    {
        $this->adapter = new adapter();
    }
}

Simple dependency injection

The coupling degree of the above code is too high, which leads to the emergence of
• Dependency Injection, mainly for decoupling
For the following cases, we only You need to pass in the class object that needs to be operated
• Dependency injection The parameters of the operation are objects, not ordinary parameters. Do you have a better understanding?
But such a simple dependency injection will cause if you depend on a lot of classes, it will take a long time when you pass parameters, which will easily
• confuse

<?php
class container
{
    private $adapter;

    public function __construct(adapter $adapter)
    {
        $this->adapter = $adapter;
    }
}

High-level dependency injection

In order to solve the above problem of
• parameter confusion, at this time, dependency injection has been optimizedThrough the magic method,
  __get Set the object
At this time, we can solve the problem of too many dependencies and confusing parameters

<?php
class container
{
    public $instance = [];

    public function __set($name, $value)
    {
        $this->instance[$name] = $value;
    }
}

$container = new container();

$container->adapter = new adapter();
$container->autofelix = new autofelix();

Dependency injection application

We first define a
• container class, which is mainly used to inject the class you want to operate
into the container. At this time, you only need to pass the
• object of the container

<?php
class container
{
    public $instance = [];

    public function __set($name, $value)
    {
        $this->instance[$name] = $value;
    }
}

class adapter
{
    public $name = '我是调度器';
}

$container = new container();
$container->adapter = new adapter();

class autofelix
{
    private $container;

    public function __construct(container $container)
    {
        $this->container = $container;
    }

    public function who($class)
    {
        return $this->container->instance[$class]->name;
    }
}

$autofelix = new autofelix($container);

$who = $autofelix->who('adapter');

var_dump($who); //我是调度器

Dependency Injection Advanced Optimization

above In the application, we
• directly inject the instantiated objects into the container
This will cause all objects to be instantiated before they are used, causing
• resource loss Loss
We can
• pass in the closure, so that the object will not be instantiated and injected. When you need to use it yourself, instantiate it again, which can reduce Loss of server resources

<?php
$container = new container();
$container->adapter = new adapter();

//高阶优化
$container = new container();
$container->adapter = function () {
    return new adapter();
};

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