Req #53648 [Com]: Allow __toString() to throw exceptions

From: Date: Thu, 10 Nov 2011 04:05:49 +0000
Subject: Req #53648 [Com]: Allow __toString() to throw exceptions
References: 1  Groups: php.bugs 
Request: Send a blank email to php-bugs+get-165007@lists.php.net to get a copy of this message 
Edit report at https://bugs.php.net/bug.php?id=53648&edit=1

 ID:                 53648
 Comment by:         dqhendricks at hotmail dot com
 Reported by:        clicky at erebot dot net
 Summary:            Allow __toString() to throw exceptions
 Status:             Open
 Type:               Feature/Change Request
 Package:            Class/Object related
 PHP Version:        5.3.4
 Block user comment: N
 Private report:     N

 New Comment:

this problem is causing me such a headache. i'm not even trying to convert an object 
to a string and i'm getting this error. the bug become such a pain to track. i have 
an active record that lazy loads child objects through __get. so even though im just 
trying to print a property of an object that is a string, the fact that a __get is 
used to get that object, prevents me from throwing exceptions. it looks like this 
echo $activerecord->childobject->somestring;


Previous Comments:
------------------------------------------------------------------------
[2011-01-04 14:45:29] clicky at erebot dot net

Description:
------------
Currently, when casting an object with __toString() to a string, __toString() is not allowed to
throw an exception.
Trying to do so triggers an E_ERROR "Method %s::__toString() must not throw an exception".
IMHO, this is counter-intuitive, especially since calling that object's __toString() method
directly would correctly throw the exception.

I propose to allow __toString() to throw exceptions.

Note: this was already reported in http://bugs.php.net/bug.php?id=50699 but marked as
bogus with the only explanation being "__toString must not throw".
So, I'm marking this as a feature request rather than a bug, since the current behaviour seems
to be expected (though it is not documented in http://php.net/manual/en/language.oop5.magic.php#language.oop5.magic.tostring).

I also found this entry http://stackoverflow.com/questions/2429642/why-its-impossible-to-throw-exception-from-tostring
which cites Johannes saying this requires major changes in the code. However, the article mentioned
is from 2007 and I think the limitations in ZE that prevented this to be implemented were lifted
since then.

I'm not very versed in PHP's inner workings, but attached is a tentative patch which seems
to fix this issue.

Test script:
---------------
<?php

class CustomException
extends Exception
{
}

class Foo
{
    public function __toString()
    {
        throw new CustomException('oops!');
    }
}


$foo = new Foo();
try {
    var_dump((string) $foo);
}
catch (CustomException $e) {
    var_dump($e);
}

?>

Expected result:
----------------
object(CustomException)#2 (7) {
  ["message":protected]=>
  string(5) "oops!"
  ["string":"Exception":private]=>
  string(0) ""
  ["code":protected]=>
  int(0)
  ["file":protected]=>
  string(17) "/tmp/toString.php"
  ["line":protected]=>
  int(65)
  ["trace":"Exception":private]=>
  array(1) {
    [0]=>
    array(6) {
      ["file"]=>
      string(17) "/tmp/toString.php"
      ["line"]=>
      int(71)
      ["function"]=>
      string(10) "__toString"
      ["class"]=>
      string(3) "Foo"
      ["type"]=>
      string(2) "->"
      ["args"]=>
      array(0) {
      }
    }
  }
  ["previous":"Exception":private]=>
  NULL
}


Actual result:
--------------
PHP Fatal error:  Method Foo::__toString() must not throw an exception in /tmp/toString.php on line
0
PHP Stack trace:
PHP   1. {main}() /tmp/toString.php:0


------------------------------------------------------------------------



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