Question

Basically this is what i want to do:

<?php
  class App {
    public $var = "main-class";
    public function load() {
      $this->var =  "child-class";
      $child = new Child;
      $child->echo_var();
    }
  }
  class Child extends App {
    public function echo_var() {
       echo $this->var;
    }
  }

  $app = new Child;
  $app->load();
?>

It outputs “main-class”, i want it to output “child-class” without having to modify the child class (because i want it to be sort of a “clean” and dynamic class).

I accept suggestions for another course of action

PS: This is part of an Small MVC Framework i’m trying to develop.

Answer 1

There are two ways that you could do this. Both are going to need to use constructors. With the first one, the child will declare itself when created

<?php
class App {
    public $var = "main-class";

    public function __construct($var=null) {
        if($var !== null) {
            $this->var = $var;
        }
    }

    public function load() {
        $child = new Child ();
        $child->echo_var();
    }
}

class Child extends App {
    public function __construct(){
        parent::__construct("child-class");
    }

    public function echo_var() {
        echo $this->var;
    }
}

$app = new Child();
$app->load();
?>

The second one allows the parent to declare the name of the child.

<?php
class App {
    public $var = "main-class";

    public function __construct($var=null) {
        if($var !== null) {
            $this->var = $var;
        }
    }

    public function load() {
        $child = new Child ("child-class");
        $child->echo_var();
    }
}

class Child extends App {
    public function echo_var() {
        echo $this->var;
    }
}

$app = new Child();
$app->load();
?>

Both of those examples work and do what you want, I believe.