Detailed explanation of the three realms of PHP decoupling

This article mainly introduces the relevant knowledge of the three realms of PHP decoupling. Has very good reference value.

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 needed Cooperation, sometimes you can also complete it independently. No matter which one it is, as the amount of code increases, it gets "out of control" every time, and gradually "ugly interfaces, dirty implementation", the cost and difficulty of project maintenance increase, and it reaches the point where it is difficult to The only degree of maintenance is reconstruction or redevelopment.

The 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();

Writing disadvantages:

1. Construct an object in a public function. Once it involves changes in database parameters, modifications will require a lot of work

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?

The second level (parameter dependency)

Hypothetical scenario: The database address needs to be changed frequently because of different customers, and the class called to DB There are many (if there are dozens), and I hope 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 to create the DB class, FileSystem class, etc. first, which 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), and then Create the writer variable he wants.

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. I hope that the DB class, Session class, and FileSystem class can be used "out of the box" without tedious initialization every time, such as writing $db=new DB(arg1, arg2);This type of statement.

#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 to 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);

##The above is the entire content of this article, I hope it will be helpful to everyone's learning.

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