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Re: Class 'Model' not found

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Matthew Carter wrote:

> Thomas 'PointedEars' Lahn <PointedEars@web.de> writes:
>> Different sites on the same machine, each using different versions of the
>> same class, perhaps in the same namespace, would either use *different*
>> autoloaders each (to avoid loading classes and their dependencies
>> manually). This can be as simple as adapting the include_path per site,
>> or as complicated as using different “require_once” statements (with
>> different paths) to load the correct autoloader.
>>
>> Or they would use one or more namespace-and-path-aware autoloaders.  It
>> is possible to register *several* autoloaders, each only attempting to
>> autoload the classes that are in its namespace.  Simple example:
>> […]
>> [Usually it does not make sense to use two versions of the same library
>> simultaneously because of different dependencies, and because the newer
>> version can do more than the older one.  However, it is probably a good
>> idea to always write an autoloader so that it does not attempt to
>> autoload classes that are "out of its jurisdiction".]
>>
>> It is also possible to have *one* autoloader that handles *several*
>> namespaces and maps namespaces to paths correctly.  Simplest (as is,
>> *unsafe*) case:
>>
>>   function autoload_all ($class)
>>   {
>>     require_once str_replace("\\", DIRECTORY_SEPARATOR, $class) . ".php";
>>   }
>>
>>   spl_autoload_register("\\autoload_all", true);
>>
>> [Note that the autoloader can be in a namespace itself, which reduces the
>> risk of namespace collisions for *its* declaration.  That also makes it
>> easier to autoload only the classes "in the autoloader’s jurisdiction".]
>>
>> IOW, the problems that you are presuming simply *do* *not* *exist*.
> 
> Great explanation, a wonderful reference for anyone needing to
> understand these topics better.

Thank you very much.

In order not to be misunderstood, I want to clarify and emphasize that 
I meant “to *load* two versions of the same library (*written in PHP*)” when 
I wrote “to use two versions of the same library”.  And when I wrote “user”, 
I meant the user of code written in PHP (i.e. a PHP programmer), not the end 
user.

“Loading” is different to “using” because AISB there can be two (or more) 
versions of a library (written in PHP) on the storage device (“using”), to 
be used by different programs/sites accessing that storage device, but you 
usually need not (and do not want to or simply cannot, due to the 
aforementioned namespace conflicts) *load* all of them at the same time, in 
the same PHP program.

One also has to keep in mind that (AISB) the include statements “include”, 
“include_once”, “require”, and “require_once” observe the “include_path” 
setting.  And the autoloader can determine its location in the filesystem 
with the __FILE__ and __DIR__ magic constants [0].  So if the library path 
or the library repository path is in the include_path (which can be set in 
php.ini, in Web server configuration files, and even on runtime by default 
[1]), everything follows from there.

Usually, the only thing that has to be and should be loaded via 
“require_once” *in user code* is the autoloader itself.  However, dependency 
managers like Composer [2] can set that up when installing a library in an 
application as a package.

The DIRECTORY_SEPARATOR in the autoloader code removes the final dependency 
on the setup of the server system because it is a constant that is set to 
what is supported by the operating system that PHP was compiled for (and 
therefore is supposed to be running on). [3]

_________
[0] <http://php.net/manual/en/language.constants.predefined.php>
[1] <http://php.net/set_include_path>
[2] <https://getcomposer.org/>
[3] <http://php.net/manual/en/dir.constants.php>

    (While the documentation confusingly says there that an extension
    has to be installed for those contants to be available,
    <http://php.net/manual/en/dir.installation.php> emphasizes that
    “There is no installation needed to use these functions; they are part 
    of the PHP core.”)
-- 
PointedEars
Zend Certified PHP Engineer 
<http://www.zend.com/en/yellow-pages/ZEND024953> | Twitter: @PointedEars2
Please do not cc me. / Bitte keine Kopien per E-Mail.

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Thread

Class 'Model' not found M desinger <info.nez@gmail.com> - 2016-08-21 07:35 -0700
  Re: Class 'Model' not found M desinger <info.nez@gmail.com> - 2016-08-21 07:36 -0700
  Re: Class 'Model' not found M desinger <info.nez@gmail.com> - 2016-08-21 07:43 -0700
    Re: Class 'Model' not found "J.O. Aho" <user@example.net> - 2016-08-21 18:08 +0200
      Re: Class 'Model' not found "Christoph M. Becker" <cmbecker69@arcor.de> - 2016-08-21 19:36 +0200
    Re: Class 'Model' not found Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2016-08-22 20:56 +0200
      Re: Class 'Model' not found Jerry Stuckle <jstucklex@attglobal.net> - 2016-08-22 19:08 -0400
        Re: Class 'Model' not found Matthew Carter <m@ahungry.com> - 2016-08-23 01:23 -0400
          Re: Class 'Model' not found Jerry Stuckle <jstucklex@attglobal.net> - 2016-08-23 08:07 -0400
            Re: Class 'Model' not found Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2016-08-27 14:26 +0200
              Re: Class 'Model' not found Jerry Stuckle <jstucklex@attglobal.net> - 2016-08-27 10:13 -0400
                Re: Class 'Model' not found Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2016-08-28 02:12 +0200
                Re: Class 'Model' not found Jerry Stuckle <jstucklex@attglobal.net> - 2016-08-27 20:32 -0400
              Re: Class 'Model' not found Matthew Carter <m@ahungry.com> - 2016-08-28 00:00 -0400
                Re: Class 'Model' not found Jerry Stuckle <jstucklex@attglobal.net> - 2016-08-28 08:40 -0400
                Re: Class 'Model' not found Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2016-08-30 11:39 +0200
                Re: Class 'Model' not found Jerry Stuckle <jstucklex@attglobal.net> - 2016-08-30 07:41 -0400
                Re: Class 'Model' not found Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2016-08-30 14:41 +0200
                Re: Class 'Model' not found Jerry Stuckle <jstucklex@attglobal.net> - 2016-08-30 09:02 -0400
                Re: Class 'Model' not found Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2016-08-30 15:36 +0200
                Re: Class 'Model' not found Jerry Stuckle <jstucklex@attglobal.net> - 2016-08-30 10:39 -0400
                Re: Class 'Model' not found Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2016-08-30 11:35 +0200
  Re: Class 'Model' not found M desinger <info.nez@gmail.com> - 2016-08-30 14:25 -0700
    Re: Class 'Model' not found Gregor Kofler <usenet@gregorkofler.com> - 2016-08-31 00:35 +0200
      Re: Class 'Model' not found M desinger <info.nez@gmail.com> - 2016-08-30 16:34 -0700
        Re: Class 'Model' not found Jerry Stuckle <jstucklex@attglobal.net> - 2016-08-30 19:58 -0400

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