PHP can nest class in two files?

Question

I know that php can't nest classes, but it seems that it can if the two classes are in two files:

MainClass.php:

<?php

ini_set('display_errors', 'On');

error_reporting(E_ALL | E_STRICT);



class mainclass

{

  private $var;

  public function __construct()

  {

    require_once ('subclass.php');

    $subinstant = new subclass();

  }

}

$maininstant = new mainclass();

And

subclass.php

<?php

ini_set("display_errors", "On");

error_reporting(E_ALL | E_STRICT);

class subclass

{

  public function __construct()

  {

    $this->var="this-var\n";

    echo $this->var;

    $test="test in construct\n";

    echo $test;

    function testvar()

    {

      //$this->var = "this-var in fun\n";

      //echo $this->var;

      $funtest="test in fun\n";

      echo $funtest;

    }

    testvar();

  }

}

No errors output, and the result is as expected. I just don't understand the

require_once

, it seems that it will include the code in

subclass.php

, so what's the difference, compared to write it directly at the same position?

What's more, how can I access the variable

$var

in

testvar()

? (Use as many methods as you can think), thanks!

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Answer 1

require_once does not include the code from the other class right on the spot. The behavior of require, require_once, include and include_once is unique: it "leaves" the current object and "merges" the code from the requested file to the global scope.

This means, that what you perceive as this

class mainclass
{
  private $var;
  public function __construct()
  {
    require_once ('subclass.php');
    $subinstant = new subclass();
  }
}

the PHP interpreter actually sees this (when you create an instance of mainclass):

class mainclass
{
  private $var;
  public function __construct()
  {
    $subinstant = new subclass();
  }
}

class subclass
{
  public function __construct()
  {
    $this->var="this-var\n";
    echo $this->var;
    $test="test in construct\n";
    echo $test;
    function testvar()
    {
      //$this->var = "this-var in fun\n";
      //echo $this->var;
      $funtest="test in fun\n";
      echo $funtest;
    }
    testvar();
  }
}
$maininstant = new mainclass();

As @Federkun pointed in the comment to this post, it's actually written in the docs:

However, all functions and classes defined in the included file have the global scope.

PHP can nest class in two files?

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