Is the __destruct method useful?

Question

I read about the method __destruct these two links:

• http://php.net/manual/en/language.oop5.decon.php
• https://stackoverflow.com/questions/7240230/is-the-destruct-method-necessary-for-php

And I still haven’t found the use of the method __destruct, even more than according to @user166390, (the user who answered the 2nd link question) said:

.."The destructor has Nothing directly to do with Releasing memory" (...A destructor has nothing to do with releasing memory directly...

According to him, it would have another purpose that I did not understand very well. Could someone give me a practical explanation of the use of __destructor? And an example where the __destructor be necessary?

Answer 1

There is, but first you have to understand at what moments it runs.

The concept is similar to other languages such as C++, the __destruct is always triggered when the reference of a "class called" is "destroyed", for example:

$test = new MinhaClasse();
$test = null; //A partir daqui o __destruct provavelmente será chamado (ou no fim do script)

If there is nothing like this in the script and the variable is accessible by other scopes, then the object will stay there until the shutdown of the script, then the __destruct will be triggered only when the script has already been completed.

When to use __destruct

Imagine that you have a series of variables in the class or variables of vectors, large and when the class is destroyed you want to clean them, then you can use the __destruct, this helps in the release of a little memory (it will depend on how the GC behaves, has no way of controlling).

class Foo {
    private $bar = array();

    public function __construct() {
         $this->bar = range(1, 1000000);//Gera um grande vetor
    }

    public function __destruct() {
         $this->bar = null;//libera variável
    }
}

You can also use this to disconnect from socket, or mysql without calling mysqli_close, for example:

class Conexao {
    private $link = null;
    public function __construct() { //Auto-conecta
         $this->link = mysqli_connect("127.0.0.1", "my_user", "my_password", "my_db");
    }

    public function __destruct() {
         mysqli_close($this->link);//desconecta
         $this->link = null;
    }
}

By calling it:

$test = new Conexao();

//...Aqui fica todo o processo que vai usar a conexão

$test = NULL; //A partir daqui provavelmente a classe será destruída

//...Outras tarefas

This way you won’t need to disconnect, the __destruct will take care of it for you.

About the comment:

.."The destructor has Nothing directly to do with Releasing memory" (...A destructor has nothing to do with releasing memory directly...

He said "immediately", meaning yes, "help" to release, but this does not occur immediately, it is used to release "references" or other tasks, such as disconnecting from a socket. The release of memory will depend on the GC as I quoted earlier.

The __destruct does not release the references automatically, it is a method that you should write yourself, in this method you will have to say how and what should be released from the "internal references" of the class, then the references being free the GC will take charge of trying to free the memory.