Re: OO PHP result of new if a constructor fails

From	"James Harris" <james.harris.1@gmail.com>
Newsgroups	comp.lang.php
Subject	Re: OO PHP result of new if a constructor fails
Date	2014-11-11 16:27 +0000
Organization	A noiseless patient Spider
Message-ID	<m3tdce$fd0$1@dont-email.me> (permalink)
References	<m3t91i$rp6$1@dont-email.me> <m3t9et$t8s$1@dont-email.me> <m3tbjo$78r$1@dont-email.me> <m3tc0l$8ic$1@dont-email.me>

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"Jerry Stuckle" <jstucklex@attglobal.net> wrote in message 
news:m3tc0l$8ic$1@dont-email.me...
> On 11/11/2014 10:56 AM, James Harris wrote:
>> "Jerry Stuckle" <jstucklex@attglobal.net> wrote in message
>> news:m3t9et$t8s$1@dont-email.me...
>>> On 11/11/2014 10:13 AM, James Harris wrote:
>>>> From what I've found I understand that PHP constructors cannot return
>>>> anything and that leads on to a specific query: if a piece of PHP code
>>>> uses
>>>> new as in
>>>>
>>>>   $a = new b();
>>>>
>>>> as long as no exception is thrown is $a guaranteed to hold something
>>>> after
>>>> the statement? Is it guaranteed to hold an object of the designated 
>>>> type?
>>>> What happens if b's constructor "fails" in some way for various 
>>>> meanings
>>>> of
>>>> failure other than throwing exceptions?
>>>>
>>>> To put it another way, after the above instantiation statement which of
>>>> these would be guaranteed to be true?
>>>> 1) $a WILL contain a b object
>>>> 2) $a could be NULL
>>>> 3) $a might not exist (if it did not before the statement)
>>>>
>>>> Or does the answer depend on the specific class or on the version of 
>>>> PHP?
>>>>
>>>> Sorry that's a lot of questions. Just trying to make the query clear.
>>
>> ...
>>
>>> The first question is - how did the constructor "fail"?
>>
>> Any way you can imagine without throwing an exception. I was hoping there
>> was a universal rule that could apply to all of PHP OO programming.
>>
>
> No, specifically - how can it fail?
>
>> If you mean that a constructor cannot fail I don't agree. If you mean 
>> there
>> are limited ways that a constructor can fail then I agree but for all and
>> any of those means of failure what would be the effect on the object so
>> constructed?
>>
>> If you want a specific, here's one.
>>
>>   $db1 = new mysqli(...);
>>   if ($db1->connect_errno...)
>>
>> The instantiation can fail in a number of ways. Which of the scenarios
>> labelled 1 to 3, above, will always be true when we reach the test
>> statement? The test will baulk on two of them.

...

> Specifically, how would the constructor fail?
>
> I'm not trying to give you a hard time.

Are you sure? .... :-(

>  You can't answer what happens
> in case of failure without understanding the failure itself.

I think you may be talking about something else. I guess there are lots of 
ways a constructor can fail: out of memory, no access to a resource, invalid 
parameter value, incompatible parameters, disk IO error, network outage, 
invalid credentials, faulty program etc etc. Without knowing the internals 
of a particular constructor (not a good idea) your question about how that 
constructor can fail cannot be answered. Even if it could the answer(s) 
might change when a new version of that constructor is released. So there is 
no way to sensibly enumerate all potential causes of failure and derive 
findings from that.

So rather than asking about a specific constructor I was looking to see if 
there was a PHP rule that could always be applied.

If that's not what you mean can you explain what you have in mind? I cannot 
understand your meaning from what you have said so far.

James

Thread

OO PHP result of new if a constructor fails "James Harris" <james.harris.1@gmail.com> - 2014-11-11 15:13 +0000
  Re: OO PHP result of new if a constructor fails Jerry Stuckle <jstucklex@attglobal.net> - 2014-11-11 10:20 -0500
    Re: OO PHP result of new if a constructor fails "James Harris" <james.harris.1@gmail.com> - 2014-11-11 15:56 +0000
      Re: OO PHP result of new if a constructor fails Jerry Stuckle <jstucklex@attglobal.net> - 2014-11-11 11:03 -0500
        Re: OO PHP result of new if a constructor fails "James Harris" <james.harris.1@gmail.com> - 2014-11-11 16:27 +0000
          Re: OO PHP result of new if a constructor fails Matthew Carter <m@ahungry.com> - 2014-11-11 12:01 -0500
            Re: OO PHP result of new if a constructor fails Jerry Stuckle <jstucklex@attglobal.net> - 2014-11-11 12:56 -0500
          Re: OO PHP result of new if a constructor fails Jerry Stuckle <jstucklex@attglobal.net> - 2014-11-11 12:52 -0500
  Re: OO PHP result of new if a constructor fails "Christoph M. Becker" <cmbecker69@arcor.de> - 2014-11-11 18:12 +0100
  Re: OO PHP result of new if a constructor fails Richard Damon <Richard@Damon-Family.org> - 2014-11-11 13:03 -0500
  Re: OO PHP result of new if a constructor fails Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2014-11-11 23:54 +0100
    Re: OO PHP result of new if a constructor fails "Christoph M. Becker" <cmbecker69@arcor.de> - 2014-11-12 03:00 +0100
      Re: OO PHP result of new if a constructor fails Matthew Carter <m@ahungry.com> - 2014-11-11 22:25 -0500
        Re: OO PHP result of new if a constructor fails Jerry Stuckle <jstucklex@attglobal.net> - 2014-11-11 22:36 -0500
          Re: OO PHP result of new if a constructor fails Matthew Carter <m@ahungry.com> - 2014-11-12 01:30 -0500
            Re: OO PHP result of new if a constructor fails Jerry Stuckle <jstucklex@attglobal.net> - 2014-11-12 07:08 -0500
            Re: OO PHP result of new if a constructor fails "Christoph M. Becker" <cmbecker69@arcor.de> - 2014-11-12 13:30 +0100
              Re: OO PHP result of new if a constructor fails Denis McMahon <denismfmcmahon@gmail.com> - 2014-11-12 13:52 +0000
                Re: OO PHP result of new if a constructor fails "Christoph M. Becker" <cmbecker69@arcor.de> - 2014-11-13 00:46 +0100
                Re: OO PHP result of new if a constructor fails Jerry Stuckle <jstucklex@attglobal.net> - 2014-11-12 22:28 -0500
      Re: OO PHP result of new if a constructor fails Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2014-11-12 21:30 +0100
        Re: OO PHP result of new if a constructor fails "Christoph M. Becker" <cmbecker69@arcor.de> - 2014-11-13 01:15 +0100
          Re: OO PHP result of new if a constructor fails Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2014-11-13 04:09 +0100
            Re: OO PHP result of new if a constructor fails Stefan+Usenet@Froehlich.Priv.at (Stefan Froehlich) - 2014-11-13 07:42 +0000
            Re: OO PHP result of new if a constructor fails "Christoph M. Becker" <cmbecker69@arcor.de> - 2014-11-13 14:11 +0100
              Re: OO PHP result of new if a constructor fails Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2014-11-13 21:40 +0100
                Re: OO PHP result of new if a constructor fails "Christoph M. Becker" <cmbecker69@arcor.de> - 2014-11-14 13:49 +0100
                Re: OO PHP result of new if a constructor fails Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2014-11-14 23:25 +0100
          Re: OO PHP result of new if a constructor fails Jerry Stuckle <jstucklex@attglobal.net> - 2014-11-12 22:29 -0500
            Re: OO PHP result of new if a constructor fails Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2014-11-13 21:45 +0100
              Re: OO PHP result of new if a constructor fails Jerry Stuckle <jstucklex@attglobal.net> - 2014-11-13 15:56 -0500
                Re: OO PHP result of new if a constructor fails Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2014-11-13 22:09 +0100
                Re: OO PHP result of new if a constructor fails Jerry Stuckle <jstucklex@attglobal.net> - 2014-11-13 21:03 -0500
              Re: OO PHP result of new if a constructor fails "Christoph M. Becker" <cmbecker69@arcor.de> - 2014-11-13 22:47 +0100
                Re: OO PHP result of new if a constructor fails Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2014-11-13 22:59 +0100
                Re: OO PHP result of new if a constructor fails "Christoph M. Becker" <cmbecker69@arcor.de> - 2014-11-18 19:02 +0100

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