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Date: Thu, 17 Oct 2013 13:45:40 +0200
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To: Joe Watkins <krakjoe@php.net>
Cc: PHP internals list <internals@lists.php.net>, Julien Pauli <jpauli@php.net>
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Subject: Re: [PHP-DEV] Assertions
From: krebs.seb@gmail.com (Sebastian Krebs)

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2013/10/17 Joe Watkins <krakjoe@php.net>

> On 10/17/2013 11:51 AM, Julien Pauli wrote:
>
>> On Thu, Oct 17, 2013 at 9:25 AM, Joe Watkins <krakjoe@php.net> wrote:
>>
>>  Morning All,
>>>
>>>          I'd like to draw some attention to how poor assertions are in
>>> PHP.
>>>
>>>          The current assertion API is not usable in my opinion; it has a
>>> considerable overhead, relies on eval(), and is generally poorly
>>> implemented.
>>>
>>>          I have done some work toward implementing assert at the Zend
>>> level, giving assertions a more modern, usable feel to them.
>>>
>>>          https://github.com/krakjoe/****php-src/compare/assert<https://github.com/krakjoe/**php-src/compare/assert>
>>> <https:/**/github.com/krakjoe/php-src/**compare/assert<https://github.com/krakjoe/php-src/compare/assert>
>>> >
>>>
>>>          This implementation of assert removes the old implementation and
>>> associated functions and INI settings, and replaces it with a single INI
>>> setting to control assertion compilation.
>>>
>>>          Failed assertions throw an AssertionException (which extends
>>> ErrorException with a severity of E_ERROR), setting the message of the
>>> exception to the expression asserted.
>>>
>>>          The syntax of assertion is the same as [all] other languages:
>>>
>>>          T_ASSERT expr ';'
>>>
>>>          This means that assert("some code here") will pass assertion
>>> causing no error, because strings are no longer treated as code, because
>>> eval is evil();
>>>
>>>          Setting zend.assertions=0 system configuration setting will stop
>>> ZEND_ASSRT compilation.
>>>
>>>          So, we have:
>>>
>>>          try {
>>>                  assert (PHP != JUNK);
>>>
>>>
>>>          } catch(AssertionException $ex) {
>>>                  printf("Assertion failed: %s\n", $ex->getMessage());
>>>                  printf("Something is horribly wrong ...\n");
>>>          }
>>>
>>>          Better, no ??
>>>
>>
>>
>> I like the idea.
>> However, there is always the debatte about if a Core feature should throw
>> an Exception or generate an error.
>> In our current system, they don't throw Exceptions but generate errors.
>> Also : someone could use a callback, and then make them throw exceptions
>> if
>> he wants to ; the callback on assertion fail, which IMO is a good feature,
>> has dissapeared in your patch.
>>
>> Julien.Pauli
>>
>>  Morning Julien,
>
>         That was brought up in IRC yesterday, someone pointed out that
> generators throw exceptions in some places (from an object method, but
> still). So it's not unprecedented, and nobody has provided reason for the
> preference to use errors over exceptions ... however, general case aside:
>
>         Throwing exceptions here makes much more sense than errors, and is
> the reason there is no need for callbacks; should you need to control the
> flow of execution or take some action because of a failed assertion you can
> catch the AssertionException and do that without cluttering ini and module
> globals in order to do it.
>
>         In general, of course, an assertion should abort execution, that's
> a bit final for PHP and runs contrary to carry-on-executing-no-matter-**what,
> which we like, on the interweb. But, should you need to take some action
> and stop that exception from bubbling to the surface you should do that
> with language constructs try/catch rather than dated callbacks, which don't
> give you the same kind of recovery options so easily, they additionally
> require a new scope, a new function entry, module globals for support, and
> ini settings to configure ...
>
>         That being said, I would rather reimplement the ability to invoke
> a callback than scrap the idea all together ... but might we have something
> a bit more PHP5 ??
>
>         assert(
>                 $expression != false ||
>                 (CONSTANT_MASK & HAS_BITS),
>                 function(){
>                         echo "oh rly?"; }
>         );
>
>         I still think it's a bit unnecessary, and this:
>
>         try {
>                 assert($expression != false ||
>                         (CONSTANT_MASK & HAS_BITS));
>
>         } catch (AssertionException $ex) {
>                 echo "oh rly?";
>         }
>

Actually if an assertion fails it means, that the application is totally
broken and cannot get recovered. The use case you describe is more like
"validation".
This means, that even if it throws an AssertionException, when you are able
to catch it and recover the process, it means, that "assert" was the wrong
choice

if (!$expression && !(CONSTANT_MASK & HAS_BITS)) {
    echo "oh rly?";
}

/**
 * @var FooObject $foo properly set up FooObject-object
 */
function getByName (FooObject $foo) {
    assert($foo->getName()); // unusable without name. You use this
function wrong. Fix your application!!!
}


>
>         Makes much more sense ... I would rather encourage or even require
> that than reimplement callbacks ... they only seemed to exist to service
> the current implementation.
>
>         In summary then, I think exceptions make more sense than errors
> and callbacks ...
>
>         So what do we think about callbacks and errors now, am I making
> any sense ??


While tinking about it: As assertions are a way to describe conditions,
that are valid _in every case_ (or else the application is unrecoverable
broken), it is somehow different from just "exeptional cases", that may be
recovered during runtime. Therefore I'd prefer "the hard with" with errors
and such. I think they are somehow comparable to compile-errors, but during
runtime. Or with a "LogicException", that isn't simply (and without side
effects) solveable by replacing the value of one variable with another one.


>
>
> Cheers
> Joe
>
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>


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