PHP: rfc:function_autoloading_v2

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====== PHP RFC: Function Autoloading ====== 

  * Version: 1.0
  * Date: 2020-07-01
  * Author: Danack, based on work Anthony Ferrara
  * Status: Draft
  * First Published at: https://wiki.php.net/rfc/function_autoloading_v2 

===== Introduction =====

This RFC proposes a new unified autoloading mechanism to allow autoloading of class types (which includes classes, interfaces and traits) and functions. Currently only class type autoloading is possible in PHP.

===== Example =====

This example shows a separate autoloader being registered for classes, 

<code php>
<?php

function classTypeAutoloader($name, $type)
{
    if ($type !== AUTOLOAD_CLASS) {
        return;
    }
    if ($name !== 'foo') {
        return;
    }

    // Being able to define classes inside a function
    // already exists in PHP and is convenient for an example 
    class foo
    {
        public function __construct()
        {
            echo "class was created";
        } 
    }
}

function functionAutoloader($name, $type)
{
    if ($type !== AUTOLOAD_FUNCTION) {
        return;
    }
    if ($name !== 'foo') {
        return;
    }
    function foo() {
        echo "foo was called";
    }
}


autoload_register('classTypeAutoloader', AUTOLOAD_CLASS);

autoload_register('functionAutoloader', AUTOLOAD_FUNCTION);

// As is currently possible, trigger class autoload 
new Foo();
//output: class was created

// The triggers the capability to autoload a function 
foo();
// output: function was autoloaded and called

</code>

===== Implementation details =====

==== Constants ====

This proposal registers the following constants:

  * AUTOLOAD_CLASS => 1
  * AUTOLOAD_FUNCTION => 2


The `AUTOLOAD_CLASS` is used for registering autoloaders for all the different types, which will be classes, interfaces and traits.

The `AUTOLOAD_FUNCTION` is used for registering autoloading for functions.


==== Userland Functions ====

This proposal adds the following functions:

=== bool autoload_register(callable $callback, int $type, bool $prepend) === 


=== bool autoload_unregister(callable $callback, int $type)  ===

This function behaves similar to the current //spl_autoload_unregister// function, and unregisters a callback that was previously registered. Note that if you registered the same callback for multiple types, this will unregister all of them unless the //$type// argument is specified.

=== array autoload_list(int $type) === 

This function will return a list of all registered autoloaders for a specific type.

=== function_exists() === 

A new optional boolean argument is added to `function_exists()` to match the behavior of `class_exists()` when it comes to autoloading functions.

==== Behavior ====  

Registering autoloaders with the new API will allow callbacks to be fired on class and function missing errors.

==== Single Type Behavior ====  

By passing a single constant to the register function, the callback will only be called for types that match (the `$type` parameter is still set, but will never vary).

<file php single_type.php>
<?php
autoload_register(function($name, $type) {
    var_dump($name, $type);
    eval("function $name(){}");
    // We don't need a switch, since we only register for functions.
}, AUTOLOAD_FUNCTION);
foo(); // string(3) "foo" int(2)
new foo(); // FATAL_ERROR as no autoloader is registered
?>
</file>

==== Multiple Type Behavior ====  

By passing a bitwise-or'd constant to the register function, the callback will only be called for types that match).

<file php multiple_type.php>
<?php
autoload_register(function($name, $type) {
    var_dump($name, $type);
    switch ($type) {
        case AUTOLOAD_FUNCTION:
            eval("function $name(){}");
            break;
        case AUTOLOAD_CLASS:
            $code = <<< CODE
            class $name
                {
                    public function __construct()
                    {
                        echo "class $name was created";
                    } 
                }
CODE;
            eval($code);
            break;
    }
}, AUTOLOAD_FUNCTION | AUTOLOAD_CLASS);
foo(); // string(3) "foo" int(2)
new foo();
?>
</file>


==== Userland Backwards Compatibility ====  

=== SPL === 

This RFC proposes to strip the current //spl_autoload_register// functionality, and make //spl_autoload_*// simple proxies for registering core autoloaders. They will function exactly as they do now, but under the hood they will be using the new interface.

This means that calls to //spl_autoload_functions()// will include any autoloader (which indicates support for //AUTOLOAD_CLASS  //) registered through //autoload_register()//. However, all autoloaders registered via //spl_autoload_register// will set the //pass_type// flag to //0//, meaning that only a single argument will be passed to the callback. This is for compatiblity.


==== C API Backwards Compatibility ====  

=== SPL === 

The autoload related SPL globals have been removed, due to the implementation being centralized.

==== Backward Incompatible Changes ==== 

=== Userland === 

There should be no user-land BC changes.

==== PECL ====  

=== EG(autoload_func) === 

PECL extensions which rely on the //EG(autoload_func)// global variable will break (due to refactor).

A quick scan of LXR shows that only the [optimizer](http://lxr.php.net/xref/PECL/optimizer/optimize.c#4660) extension would change.

=== autoload_func_info === 

PECL extensions which reply on the SPL type //autoload_func_info// will break (due to refactor).

A quick scan of LXR shows that no extensions use this.

=== SPL_G(autoload_functions) === 

PECL extensions which rely on the SPL globals will break (due to refactor).

A quick scan of LXR shows that no extensions use this.

==== Proposed PHP Version(s) ==== 

PHP 8.0

==== SAPIs Impacted ==== 

None.

==== Impact to Existing Extensions ==== 

See Backward Incompatible Changes

==== php.ini Defaults ==== 

None.

==== Open Issues ==== 

None yet.


==== Future Scope ====

A previous version of this RFC included support for autoloading constants and streams. These have been excluded from this RFC for the following reasons.

=== Constant autoloading ===

Although it would be possible to add constant autoloading, the position of this RFC is that being unable to directly reference [[https://github.com/Danack/RfcCodex/blob/master/referencing_functions.md|functions by name]] is a more important problem to address.


If we added constant autoloading now, that would have a very high chance of limiting the choices surrounding being able to reference functions. Because of that, this RFC does not include constant autoloading.

=== Stream autoloading ===

Stream autoloading is excluded from this RFC to reduce the size of the RFC. It would be possible to add it in a later version.


=== Other types ===

At some point PHP may support types other than classes as parameter, return or property types. For example perhaps enums:

<code php>
enum Compass {
  North, South, East, West 
}

function foo(Compass $direction) { ... }

foo(Compass::East);

</code>

Or typed callables:
<code php>
type logger = callable(string $message): void;

// Use that type 
function uses_logger(logger $fn) {...}

</code>

It should be possible to add to autoloading.

As PHP cannot determine what type a parameter, return or property type will be before it is loaded, the loading of those types will need to go through the same mechanism that is used for class autoloading. 

At that point it would make sense to either rename `AUTOLOAD_CLASS` to be `AUTOLOAD_TYPE` or more likely, add a new constant with the same value, leaving `AUTOLOAD_CLASS` as legacy.


<code php>
autoload_register('callableTypeAutoloader', AUTOLOAD_TYPE);

function callableTypeAutoloader($name, $type)
{
    if ($type !== AUTOLOAD_CLASS) {
        return;
    }
    if ($name !== 'logger') {
        return;
    }

    type logger = callable(string $message): void;
}

</code>


==== Patches and Tests ====

A patch will be created before voting.

==== Vote ====  

Accept the RFC yes/no.

==== References ==== 

  * Importing namespaces: http://php.net/manual/en/language.namespaces.importing.php
  * SPL Autoloading: http://php.net/manual/en/language.oop5.autoload.php
  * Previous RFC for function autoloading: https://wiki.php.net/rfc/function_autoloading
  * Previous pull-request: https://github.com/ircmaxell/php-src/tree/function-autoloading-7
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