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Date: Mon, 19 Jan 2015 18:04:32 +0100
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To: Ferenc Kovacs <tyra3l@gmail.com>
Cc: Dan Ackroyd <danack@basereality.com>, PHP Internals <internals@lists.php.net>, 
	Stanislav Malyshev <smalyshev@gmail.com>
Content-Type: multipart/alternative; boundary=089e013c6672f7541d050d0450f6
Subject: Re: [PHP-DEV] Class constructor behaviour
From: mike@php.net (Michael Wallner)

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On 19 Jan 2015 12:30, "Ferenc Kovacs" <tyra3l@gmail.com> wrote:
>
> On Mon, Jan 19, 2015 at 6:41 AM, Stanislav Malyshev <smalyshev@gmail.com>
> wrote:
>
> > Hi!
> >
> > > This is pretty horrible and should be fixed by making sure that
> >
> > I don't see why it's so horrible. In fact, handling null is easier than
> > handling exception (and faster too, probably). Many functions that try
> > to create objects return null or false when unable to. Of course, we
> > could change it by introducing exceptions to core, but I don't see why
> > do it peacemeal then.
> >
> > > constructors either return an object or throw an exception.
> > > Additionally the exception policy for core (that was previously
> > > discussed here: http://marc.info/?t=119263748000001&r=1&w=2 ) should
> > > be updated so that any constructor returning NULL is considered a bug,
> > > no matter what the ini settings are. To be clear, procedural code
> > > should behave as before, with users expected to check for errors.
> > > This would be a BC break for people who are handling the constructor
> > > returning null currently, as they would need to wrap that code with an
> > > try/catch block.
> >
> > That means the same failure of collator construction now needs to be
> > handled in two different ways.
> >
> > > Constructors give warning, but are then in an unusable state
> > > ------------------------------------------------------------
> > > Several constructors check the parameters that they are given.....and
> > > then just give a warning when they are not acceptable. e.g.
> >
> > These should be fixed to either return null or throw exception, but the
> > behavior should be unified for everybody.
> >
> > > Again, this should be fixed by changing the constructors to throw an
> > > exception if the input parameters are not acceptable.
> >
> > The next question would be - if the ctors throw an exceptions, why
> > factory methods shouldn't? They are doing the same work essentially.
> >
> > > Constructor gives error
> > > -----------------------
> > >
> > > Some constructors check the parameters they are given, and then emit
> > > either a 'Catchable fatal error' error or other error e.g.
> >
> > This is even bigger can of worms. If we wrote PHP today from scratch,
> > catchable fatal errors would be exceptions. But they are not, so we need
> > to deal with it - by either leaving them as is, or converting them all
> > together.
> >
> > >
> > > <?php
> > > $foo = new IntlGregorianCalendar(new StdClass);
> > > //Output: Catchable fatal error: Object of class stdClass could not be
> > > converted to string in..
> >
> > This is not property of the ctor, it's property of parameter handling.
> > I.e. if you do it for IntlGregorianCalendar, you should do it for every
> > class that gets incompatible parameters. And probably user-space funcs
> > too since there's no reason for them to behave differently. I actually
> > wouldn't mind that, but this is yet bigger can of worms as it requires
> > refactoring a lot of assumptions on how parameters are parsed.
> >
> > > i) Can anyone see a big hurdle in fixing these behaviours, other than
> > > it being a BC break for people who are currently relying on these
> > > behaviours ?
> >
> > Yes. The first hurdle is to understand which of these behaviors need
> > fixing, and how, which you seem to dismiss as obvious but it's really
> > not. The second is to do it in consistent manner so it doesn't again
> > come out as part of the functions do one thing, another part another,
> > and third part something else different.
> >
> > > ii) Are there any other bad behaviours that people are aware of that
> > > ought to be fixed at a major version?
> >
> > I think we have enough for now to discuss here, so if we want do discuss
> > other behaviors better to open separate thread.
> >
> > --
> > Stas Malyshev
> > smalyshev@gmail.com
> >
> > --
> > PHP Internals - PHP Runtime Development Mailing List
> > To unsubscribe, visit: http://www.php.net/unsub.php
> >
> >
> Hi,
>
> AFAIK (based on
> http://www.mail-archive.com/internals@lists.php.net/msg43237.html and
other
> discussions) errors in constructors should throw exceptions (even for
> classes in core).
>

Definitely my take on this, too. If userland constructors cannot return
anything than an instance of the class, why should internal?

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