force PHP to throw an error on undefined property

Question

This will throw an error:

class foo
{
   var $bar;

   public function getBar()
   {
      return $this->Bar; // beware of capital 'B': "Fatal:    unknown property".
   }

}

But this won't:

class foo
{
   var $bar;

   public function setBar($val)
   {
      $this->Bar = $val; // beware of capital 'B': silently defines a new prop "Bar"
   }

}

How can I force PHP to throw errors in BOTH cases? I consider the second case more critical than the first (as it took me 2 hours to search for a d....ned typo in a property).

and what if it isn't? I still don't know that Bar isn't defined in the class. — Axel Amthor
– Axel Amthor, Commented Jun 21, 2013 at 13:18
Well, choose CamelCase or lowercase (or some other convention) and then stick with it. You can use something like PHP CodeSniffer (phpcs) to enforce it. Also, erroneous variable names will give you a perfectly understandable error message, which you can use to quickly find out where the error occurred. Using the magic methods __get and __set may solve the problem, but at what cost? It will slow down the code, and it may give rise to another set of problems. — Sverri M. Olsen
– Sverri M. Olsen, Commented Jun 21, 2013 at 13:33

Community · Accepted Answer · 2020-06-20 09:12:55Z

15

You can use magic methods

__set() is run when writing data to inaccessible properties.

__get() is utilized for reading data from inaccessible properties.

class foo
{
   var $bar;

   public function setBar($val)
   {
      $this->Bar = $val; // beware of capital 'B': silently defines a new prop "Bar"
   }

   public function __set($var, $val)
   {
     trigger_error("Property $var doesn't exists and cannot be set.", E_USER_ERROR);
   }

   public function  __get($var)
   {
     trigger_error("Property $var doesn't exists and cannot be get.", E_USER_ERROR);
   }

}

$obj = new foo(); 
$obj->setBar('a');

It will cast error

Fatal error: Property Bar doesn't exists and cannot be set. on line 13

You can set Error Levels according to PHP error levels

edited Jun 20, 2020 at 9:12

CommunityBot

11 silver badge

answered Jun 21, 2013 at 13:19

Robert

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7 Comments

Axel Amthor Over a year ago

Working, but not what I'm looking for, actually: Both answers need to add code to the class in order to programmatically check syntax for errors. You need to add that to all classes (or inherit from somewhere), not the elegant way. Never the less: upvote, I'll consider this

Robert Over a year ago

There's no other way ;/ you can always inherit it from abstract class or use traits I don't see anything that is not elegant in it.

Axel Amthor Over a year ago

Got it. I still do not regard this as "elegant", but it's worth a try (and related to PHP and not to your answer!)

Tyler Collier Over a year ago

@AxelAmthor If you have PHP 5.4+, you could use Traits (like a mix-in) rather than inheritance.

Robert Over a year ago

it could be done with traits however personally I don't like them :)

|

TimWolla · Accepted Answer · 2013-06-21 13:19:10Z

11

One solution I can imagine would be (ab)using __set and maybe property_exists:

public function __set($var, $value) {
    if (!property_exists($this, $var)) {
        throw new Exception('Undefined property "'.$var.'" should be set to "'.$value.'"');
    }
    throw new Exception('Trying to set protected / private property "'.$var.'" to "'.$value.'" from invalid context');
}

Demo: http://codepad.org/T5X6QKCI

answered Jun 21, 2013 at 13:19

TimWolla

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2 Comments

Robert Over a year ago

You were a bit faster :) beacuse I wrote more complicated example with errors not exceptions

Alexander Behling Over a year ago

@TimWolla You are not abusing the __set function. This "magic" method was defined for this. But you should not use Exception use a derived type of it. The question is which should be used. I'm unsure but I tend to use the OutOfBoundsException. see stackoverflow.com/questions/8193798/…

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