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#1 Dec. 6, 2010 19:39:58

Loon, R.
Registered: 2009-11-02
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RFC __autodefine / spl_autodefine


RFC __autodefine / spl_autodefine

This proposal proposes to introduce one function for automagically
defining missing definitions at run time.
The reader should have a reasonable level of PHP knowledge and
computer languages when reading this proposal.
Note: Whenever __autodefine is used, also spl_autodefine is meant.

Current situation

PHP currently supports defining missing classes by the __autoload function.
This solution mimics the class loader concept from Java.
Once defined, undefined class functions (methods) can be emulated by
using __call and __callStatic.
It can be argued that __autoload is enough for the future if the
future is object-oriented.


Proposition

While very useful in its own right __autoload is limited: only classes
can be loaded dynamically.
However, there is still a lot of code that is either mixed functional
and object-oriented or only functional.
Excluding that code from such a solution makes life very hard on
everyone maintaining mixed code bases.
It is understandable that by denying this function to non-object
oriented code an incentive exists for maintainers and developers to
switch to object-oriented programming.
Although understandable it is not acceptable, for the following reasons:
1) There are enough people maintaining and writing code in a perfect
manner that do not grasp object orientation
2) Any large code base should have the possibility to slowly migrate
and not be coerced into an object oriented way of working
3) Even if this coercion would work, it would not guarantee the
solution is object-oriented, only that it is coded in classes

So, it can be stated that a number of language constructs are missing
the option to autoload.

>From a conceptual point, tokens in a sequence of statements refer to
definitions. The implementation of almost all run time environments
demands that a definition exists before first referenced. __autoload
changed this rule by allowing classes to be defined when the execution
of a statement hits on an undefined class. This behaviour should be
generalized.

Generally, it can be said that PHP needs a mechanism for automagically
defining undefined elements. The proposed name for that function is
__autodefine. The parameters to this function would be $name and
$type. The type parameter would refer to all the existing elements
that are defined. Probably the maximal set of language constructs that
could be supported are: T_ARRAY, T_CLASS, T_CLASS_C, T_CONST,
T_FUNCTION T_FUNC_C, T_INCLUDE, T_INCLUDE_ONCE, T_INTERFACE,
T_METHOD_C, T_NAMESPACE, T_NS_C, T_REQUIRE, T_REQUIRE_ONCE, T_USE,
T_VAR, T_VARIABLE. The author believes the minimal solution should
support at least T_FUNCTION, T_CLASS, T_INTERFACE and include
(T_INCLUDE, T_INCLUDE_ONCE, T_REQUIRE, T_REQUIRE_ONCE). Namespaces
will be part of the name as is the case in call_user_func.

The relation with the current implementation is that __autoload equals
__autodefine( $name, T_CLASS ) with the exception of the optional
file_extensions parameter. __autoload need not be changed and
__autodefine can live alongside __autoload. Author believes __autoload
should be marked 'deprecated'.


Minimal solution proposal

__autodefine( $name, $type )

$name is the string of the missing definition

$type is the integer identification of the type and defined by constants.


$type constant $name format
name examples

T_FUNCTION function name
a\b\foo, System::boot, SomeClass->getWidth
T_CLASS class name
Image, ns\Image
T_INTERFACE class name Image, ns\Image
T_INCLUDE file name
somefile, ../somefile, \includes\Somefile
T_INCLUDE_ONCE file name
somefile, ../somefile, \includes\Somefile
T_REQUIRE file name
somefile, ../somefile, \includes\Somefile
T_REQUIRE_ONCE file name
somefile, ../somefile, \includes\Somefile


Code examples

foo(b); // __autodefine( 'foo', T_FUNCTION )

p = new PHP(); // __autodefine( 'PHP', T_CLASS )

include 'piece' // __autodefine( 'piece', T_INCLUDE )

ons\foo(); // __autodefine( 'ons\foo', T_FUNCTION )

p->im(); // __autodefine( 'PHP->im', T_FUNCTION )

p->cm(); // __autodefine( 'PHP::cm', T_FUNCTION )


Advantages

A whole new array of possibilities opens up for managing code, both at
run time and both at design time (development). Code is no longer
bound to file containers. Small pieces of code can exist on their own.
At run time only the code pieces that are needed for execution are
defined. No longer parsing of complete files when only 5 code lines
will be executed. A parse error in a file not relevant to the piece of
code that will be executed will not prevent execution anymore. By
splitting code up, developers can work side by side on the same code
base, every developer on a set of code pieces, much smaller than the
files now and thus reducing (locking) conflicts. Code pieces can be
tested standalone and accepted. Progress is measurable on function
level. Requirements can be tied to their functions. Basically, a lot
of metafunctions are suddenly possible because splitting up code in
smaller pieces has become a workable solution. Code could be for
example managed like in a wiki, with page (= code piece) revisions
etc. If needed the code pieces can be assembled into any number of
files for delivery. An extreme solution is assembling all the code
pieces into a zip file and having a run time implementation of
__autodefine that picks definitions from a zip file. While the same
code is available during development in a wiki. Large codebases can be
split up over time into more manageable pieces giving the developers
renewed control over their application. The __autodefine function will
enable all sorts of new ways of managing code and work processes.
Security can be enhanced enormously as it is not common anymore where
definitions will come from and how they are decrypted. Even if someone
gets access to the source code (outside the web root), it might be
scrambled. Also insight into the system can be obtained by observing
definition patterns that can be gathered during the autodefine
processing.


Disadvantages

Initially execution may be slower. However, this can be countered with
different implementations for __autodefine at production time and
development time. The author also believes that others will find ways
to counter this disadvantage by using caching or keeping definitions
in memory inbetween executions.


Conclusion

The minimal solution to support all definitions would be the function
__autodefine( $name, $type ). From there on, every developer can
determine his/her own strategy for automagically defining
implementations. The __autodefine function enables developers to split
code up into smaller pieces as before while at the same time make it
manageable by removing the need to include all these functions. By
splitting code up in smaller pieces more developers can work together
on one (1) code base. A parse error in a function that is not called
will not damage the run time as is the case in the current
implementation where many functions are grouped into files for reasons
of manageability. __autodefine also enables developers to utilize all
sorts of autodefinition mechanisms like retrieving definitions from
the file system, the network, a zip file or even a database. Even
multiple sources can be used, runtime versioning mechanisms can be
utilized, code decryption on the fly is possible. It would be even
interesting if the autodefinition could be in the form of byte codes.

The __autodefine function is generic enough that the same concept can
be applied in most other languages.

The request is to supply at least the minimal __autodefine in a very
near future version of PHP. To be complete and consistent spl_
autodefine_ call, spl_ autodefine_ extensions, spl_ autodefine_
functions, spl_ autodefine_ register, spl_ autodefine_ unregister and
spl_ autodefine should be defined (although considered not necessary
according to the author).

Reinier van Loon

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#2 Dec. 8, 2010 11:10:55

Loon, R.
Registered: 2009-11-02
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RFC __autodefine / spl_autodefine


All, I made a RFC in the Wiki for autodefine.http://wiki.php.net/rfc/autodefineCheers, Reinier

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#3 Dec. 8, 2010 12:12:27

Loon, R.
Registered: 2009-11-02
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RFC __autodefine / spl_autodefine


> __autoload() works fine if you have exactly one implementation for your entire
> system with exactly one set of logic for how to map a class name to a file
> name. As soon as you try to mix two different libraries together, fatal
> error.
>
> spl_autoload() does not suffer from this short-sighted problem but
> accomplishes the same goal in a much more robust fashion.
>
> Any new meta-auto-load mechanism should forego the dead-end that is a single
> unique __auto*() function and just use a design that actually works, aka
> spl_autoload() or similar.

I see the problem. At projectpier.org we have the one code set situation.
Given the reactions, I will rewrite the RFC to use spl* functions with
the information supplied above.

> With that said, I like the idea of generalizing autoload to include functions
> et al. Autoloading functions would make my life a lot easier. :-)

Yes, the alternative solution is to write a wrapper function:
somefunc($a, $b) becomes ppcall("somefunc", $a, $b)
Works but if we can get this in PHP itself it will be much better.

>To be fair, though, half of the potential benefits the OP listed are already
>solved
> by using a version control system. Any version control system. If you're
> still having collisions at the file level when two people work on the same
> file it's because you're an idiot and are not using version control (or the
> changes touch each other, in which case this proposal wouldn't help you
> anyway).

I disagree (but otoh, I am an idiot :-)). I just think there is no
conceptual need to group functions into a file.
I also don't believe in distributed vcs (probably idiotic again :-)).
The problem of integrating code is simply postponed with a dvcs.
At work we have good experiences with a centralized code repository
where people can work together, where backups are taken care of and
were revision history is built in. Integration issue are solved before
the code is touched.
Also, I think it is crazy I have to do a grep on a filesystem to find
out in which file a function is defined (e.g. grep -i -l "ion
pick_date_widget"). I know, documentation etc. But that argument only
works when a system is in good shape when you take over. Why can't I
just see by the file name what definition hides inside?

> The main advantage of this proposal would be lazy-loading of functions.
> I don't think autoloading methods makes any sense since classes cannot be
> split between files anyway.

I think I was not clear with my remark on __call and __callStatic. I
think autodefining of methods is already possible by using __call and
__callStatic for that. The __call is used in this example for
dynamically adding methods to a class:http://www.php.net/manual/en/function.call-user-func.php#89636. The
same __call function can be used to dynamically add code to the class.
But I think it would be better if the run time would do this in a
uniform way via autodefine.
The minimal definition in my view for a class would be "class
SomeClass {}" or "class SomeClass;" . But then classes resemble
namespaces to much (but in my view a class can also be viewed as a
namespace for a set of variables and functions). This is however
getting to theoretical, so lets keep it simple and let's assume that
the minimal definition of a class should have its variables, like this
"class SomeClass { var a; var b; }" and that methods can be added
dynamically.

> I'm not entirely sure what else is actually reasonable to autoload. Classes,
> Interfaces, Functions, and Traits make up the scope of first-class code
> structures, don't they? Autoloading a variable doesn't even make sense to me,
> and include files are already handled by include.

Autodefining variables does make sense. Suppose you have a variable
called "$language" which is an array with a lot of language items and
that you have put this array somewhere. Current practices forces you
think what the possible paths are how the variable is accessed and
then include this array at the proper places. So far so good. But
things change in time and code is added to the system and suddenly the
variable is referenced via a path which was not foreseen. Current
practice forces you to rethink the include locations. But what happens
in reality? Most people simply include all the files somewhere
upfront, just to be sure. Again a lot of code parsed and processed
which may not be executed. Wouldn't it be much more elegant to define
the variable when it is first referenced?
Of course, this could be emulated with a function that would be
autodefined, so that is why I chose the minimal solution to not have
variables autodefined.

But another interesting option for autodefining variables is that you
are able to track which variables are used in your application. The
fun thing is that you can do this in every environment. For
development it is interesting to see if you are using variables which
you don't recognize (typo's) or don't want to use (e.g.
$HTTP_POST_VARS), for testing it is interesting to see if your test
cases are using the most important variables and for production it is
interesting to see which variables are used at all and which never.
The paragraph above applies of course to all objects that can be
autodefined. As pointed out in the RFC, autodefine enables you to get
more insight and thus more control over your codebase.

The include and include_once are simply mentioned because they are
already identified by the parser. And there is a difference between
the two. Maybe you want to know that an include_once is called
multiple times to rethink the location of the include.

Thanks for all the feedback so far. It is much easier for me to react
to arguments and remarks then to come up with answers / ideas when
writing an RFC.

Cheers, Reinier

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