Question

I spent more than 10 hours to find out the typo for debugging my PHP program. I expected PHP would produce an error when using an undefined variable. But when it is used as an object in a method, it doesn’t. Is there a reason for it?

<?php

    $oClass = new MyClass;
    // $oCless->tihs('key', 'taht');    //<-- triggers the error: Notice: Undefined variable
    $oClass->tihs('key', 'taht');
    echo $oClass->arr['key'];

    class MyClass {
        public $arr = array('key' => 'foo');

        function tihs($key, $value) {
            $tihs->arr[$key] = $value;  //<-- this does not cause an error message.
        }
    }
?>

Answer 1

Normally if the error reporting level is set to E_ALL | E_STRICT (or E_ALL as of PHP 5.4.0) it should spit out an E_STRICT error. For instance, this code:

error_reporting(E_ALL | E_STRICT);
$tihs->adrr = 453;  

Produces:

Strict Standards: Creating default object from empty value in [...]

Interestingly enough, if you specifically create an array instead of an ordinary variable as a property of an object that doesn’t exist, e.g.:

error_reporting(E_ALL | E_STRICT);
$tihs->adrr[25] = 453;  

No strict standards error is shown! It looks like this could potentially be something PHP folks might want to fix, because I’m not aware this is documented nor I think there’s a legitimate reason for this behaviour.

For the record, in both cases regardless of the error a new stdClass is being created on the fly instead, like sberry mentions in his answer.