Dynamically calling classes

Question

class App 
{
    public function __construct()
    {
        echo "app is now running...\n";
        $this->getModel('Something');
    }

    public function getModel($name)
    {
        return new $this->getModelInstance($name);
    }

    protected function getModelInstance($name)
    {
        return 'Model_' . $name;
    }
}

I have autoloader set-up and working. Why can't I load Model_Something this way, but I get the following error in return:

Notice: Undefined property: App::$getModelInstance in C:\Apache24\htdocs\ProjectName\app\App.php on line 13

Fatal error: Class name must be a valid object or a string in C:\Apache24\htdocs\ProjectName\app\App.php on line 13

score 2 · Accepted Answer · 2014-07-21 21:44:13Z

2

Try this :

public function getModel($name) {
  $modelInstanceName = $this->getModelInstance($name);
  return new $modelInstanceName();
}

---
The right way to instantiate a class is :

new Classname($parameter);

So when you were doing this :

new $this->getModelInstance($name);

The class' name was :

$this->getModelInstance

So it was looking for the getModelInstance attribute (and not function) in your App class, which doesn't exist.

edited Jul 21, 2014 at 21:44

answered Jul 21, 2014 at 21:33

user3849602

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7 Comments

user3849602 Over a year ago

I am trying to find the documentation concerning this, I do not want to explain this with wrong words. If someone else can, do not hesitate!

Félix Adriyel Gagnon-Grenier Over a year ago

@caCtus not exactly, it's more as if your were calling new [whatever string is returned by getModelInstance()]

user3849602 Over a year ago

@Félix : Why the Undefined property: App::$getModelInstance error and not a Class 'Model_Something' not found error then? (Model_Something is the string returned by getModelInstance() function here) That is how I understood the issue but maybe I am wrong (and maybe PHP tried to do the best it could in this case).

Jonathan Kuhn Over a year ago

just another explanation, what is happening is that it is trying to create an instance for the property getModelInstance and ($name) is try to call that instances constructor. So if there was a getModelInstance property with the value foo, you are essentially saying new foo($name). Since the property doesn't exist you are saying new {null}($name);. Saving the output to a variable will get you the string as a return which you can call new $string with no problem. I tried stuff like wrapping with parens or braces (which usually works) with no luck.

user3849602 Over a year ago

Also when I tried to solve the problem, I tried new $this->getModelInstance($name)(), but syntax error (same with braces). I have to admit I saw the problem, I saw how to solve it but can't explain clearly why, I don't like it. :) Thanks for your help. @Félix @Jonathan

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