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Date: Thu, 22 Jan 2004 20:29:07 +0100
Reply-To: Marcus Boerger <helly@php.net>
Message-ID: <42-1581965687.20040122202907@marcus-boerger.de>
To: Stephane Drouard <stephane.drouard@st.com>
Cc: internals@lists.php.net
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Subject: Re: [PHP-DEV] Exception / trace member
From: helly@php.net (Marcus Boerger)

Hello Stephane,

if this is really the case, well then i am the one to blame. I'll have a
look.

Thursday, January 22, 2004, 3:46:13 PM, you wrote:

> The current implementation of class Exception has a private "trace"
> member, which is used to store the backtrace. But if you throw an
> exception of a derived class of Exception, print_r() displays an empty
> "trace:private" member, as well as a "trace" (public) member that really
> holds the backtrace.

> I deduce that the backtrace is executed/stored at the derived class
> level, explaining why a new public member is created.
> Curriously, I have also noticed that "getTrace()" returns the public
> one, not the private one as expected.

> This is not to report a bug, but to ask you not to fix it as it was
> intended ("trace" member as private). Indeed I use this "feature" (being
> able to modify the trace member) to hide an intermediate call:

> <?
> class SystemException extends Exception {
>   function __construct($message, $code) {
>     parent::__construct($message, $code);
>     // Hide trace of handler() call.
>     array_splice($this->trace, 0, 1);
>     $this->file = $this->trace[0]['file'];
>     $this->line = $this->trace[0]['line'];
>   }

>   static function handler($code, $message) {
>     throw new SystemException($message, $code);
>   }
> }

> set_error_handler(array('SystemException', 'handler'));
?>>

> That way, the reported error focuses on the real file and line, not on
> the uninteresting intermediate handler call.

> In the current Exception class implementation, if both the "trace"
> member is private and getTrace() is final, it would be impossible to
> override the default behaviour. As a result, we would do our own exception
> base class, which goes against code reuse: need to redo all the things
> already done, just because the proposed class is not too open.

> A second consequence, is that each time you use code you've got from
> "outside", it could implement its own exception base class, not using the
> provided Exception. If so, we won't be able to write generic code that
> guaranties to catch all exceptions (C++ "catch(...)" or Java "finally" not
> implemented in PHP5, so need to specify a class for catch).

> The last point suggests me that PHP should guaranty that all thrown
> exceptions derive from Exception. It could be done in 2 ways:

> 1/ a fatal error when executing "throw new ...".
> Problem: it's not easy to simulate all error conditions, so we may
> deliver code that was never tested on all its "throw" branches. As a
> result, the script will stop on a fatal error, even though it was intented
> to catch and handle exceptions in a clean way.

> 2/ even if the class is not explicitly derived from Exception, throwing
> it will make it derived from Exception.
> Problem: an object of such a class will be an instance of Exception only after being thrown.

> The 2nd is my prefered one, even if I understand it could not be so easy to implement.

> One word about private and final: I don't think it's good programming
> to use them, except for security reasons. Not using them allows classes to
> be easily extended, in different directions, which is the goal of OOP.
> Moreover, all members should be protected, not public, and accessed
> through (virtual) methods, which guaranties that everything can be
> overriden if needed.

> Regards,
> Stephane




-- 
Best regards,
 Marcus                            mailto:helly@php.net