Deep into the three realms of PHP decoupling (a brief discussion of service containers)

Before reading this article, you need to master: PHP syntax, Object-oriented

In the process of completing the development of the entire software project, sometimes multiple people are required to cooperate, and sometimes You can also complete it independently. No matter which one it is, as the amount of code increases, it gets "out of control" and gradually becomes "uglyinterface, dirty implementation", and the cost and difficulty of project maintenance increase. , to the extent that it is unsustainable, the only option is to reconstruct or re-develop.

First Realm

Hypothetical scenario: We need to write a processing class that can operate sessions, databases and file systems at the same time. We might write this.

Realm characteristics: It can run, but it is severely coupled

class DB{
	public function DB($arg1,$arg2){
		echo 'constructed!'.PHP_EOL;
	}
}

class FileSystem{
	public function FileSystem($arg1,$arg2){
		echo 'constructed!'.PHP_EOL;
	}
}

class Session{
	public function Session($arg1,$arg2){
		echo 'constructed!'.PHP_EOL;
	}
}

class Writer{
	public function Write(){
		$db=new DB(1,2);
		$filesystem=new FileSystem(3,4);
		$session=new Session(5,6);
	}
}

$writer=new Writer();
$writer->write();

Disadvantages of writing:

1. Construct the object in the public function. Once it involves changes such as database parameters, modify There will be a lot of workload

2. The person responsible for designing the Writer class needs to be familiar with various APIs of DB and other classes

Is there any way to reduce the coupling?

Second level (parameter dependency)

Hypothetical scenario: The database address needs to be changed frequently due to different customers, and there are many classes that call the DB (if there are dozens ), hoping that even if the database address is changed, the code of these classes will not need to be modified.

class DB{
	public function DB($arg1,$arg2){
		echo 'constructed!'.PHP_EOL;
	}
}

class FileSystem{
	public function FileSystem($arg1,$arg2){
		echo 'constructed!'.PHP_EOL;
	}
}

class Session{
	public function Session($arg1,$arg2){
		echo 'constructed!'.PHP_EOL;
	}
}

class Writer{
	protected $_db;
	protected $_filesystem;
	protected $_session;
	public function Set($db,$filesystem,$session){
		$this->_db=$db;
		$this->_filesystem=$filesystem;
		$this->_session=$session;
	}
	public function Write(){
		
	}
}

$db=new DB(1,2);
$filesystem=new FileSystem(3,4);
$session=new Session(5,6);

$writer=new Writer();
$writer->Set($db,$filesystem,$session);
$writer->write();

Although the construction of the DB class has been moved to the client, once modifications are involved, the workload is greatly reduced, but a new problem arises: in order to create a Writer class, we need First create the DB class, FileSystem class, etc. This is very demanding for the person responsible for the Writer class. He needs to read many other class documents and create them one by one (may also need to be initialized) before he can create them. The required writer variable.

So, we hope that there will be a better way of writing, so that people who write the Writer class can use a faster interface to create and call the class they want, without even filling in the parameters. .

The third realm (IOC container)

After the first two realms, we hope to add the following benefits:

1.Hope The DB class, Session class, and FileSystem class are "ready to use" without tedious initialization every time, such as writing statements such as $db=new DB(arg1,arg2);.

2. It is hoped that DB and other types of objects are "global" and can be called at any time during the entire program running.

3. Programmers who call DB and other types do not need to know too many details of this class, and can even use a string alias to create such an object.

What can achieve the above goals is the IOC container. You can simply regard the IOC container as a global variable, and use an associative array to bind the string and the constructor.

We first implement a container class

class Container{
	public $bindings;
	public function bind($abstract,$concrete){
		$this->bindings[$abstract]=$concrete;
	}
	public function make($abstract,$parameters=[]){
		return call_user_func_array($this->bindings[$abstract],$parameters);
	}
}

Service registration (binding)

$container=new Container();
$container->bind('db',function($arg1,$arg2){
	return new DB($arg1,$arg2);
});

$container->bind('session',function($arg1,$arg2){
	return new Session($arg1,$arg2);
});

$container->bind('fs',function($arg1,$arg2){
	return new FileSystem($arg1,$arg2);
});

Container dependency

class Writer{
	protected $_db;
	protected $_filesystem;
	protected $_session;
	protected $container;
	public function Writer(Container $container){
		$this->_db=$container->make('db',[1,2]);
		$this->_filesystem=$container->make('session',[3,4]);
		$this->_session=$container->make('fs',[5,6]);
	}
}

$writer=new Writer($container);

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