PHP RFC: Function Autoloading v4

• Version: 1.0
• Date: 2024-08-15
• Author: Robert Landers, landers.robert@gmail.com
• Status: Under Discussion (or Accepted or Declined)
• First Published at: http://wiki.php.net/rfc/function_autoloading4

The topic of supporting function autoloading was brought up many times in the past, this RFC introduces a potential implementation which would be consistent with what we have for autoloading classes.

By using autoloaders, programmers can already get quickly up to speed when it comes to classes, but the language currently lacks a way to do the same for functions. This requires programmers to manually (and carefully) include files that must be included on every request. For 'functional' codebases, they lose the ability to use autoloaders, or they must write their functions as static methods on classes. This isn’t ideal, and this RFC seeks to close the gap between functions and classes.

This RFC proposes to add two new constants to the SPL extension: SPL_AUTOLOAD_CLASS, SPL_AUTOLOAD_FUNCTION. These constants may be passed to spl_autoload_register as the fourth parameter to register an autoloader for classes or functions, respectively. If not specified, the default value SPL_AUTOLOAD_CLASS will be used to retain backward compatibility.

There won’t be any changes to the current autoloading mechanism when it comes to classes.

The function autoloader will be called with the fully qualified undefined function name. This will allow the function autoloader to determine how to load or generate the function.

PHP allows programmers to call an unqualified function name. Traditionally, this means that PHP would first search in the current namespace for the function and then fall back to the global namespace if the function is not found. This behavior will be preserved. However, the function autoloader will be called only once for the current namespace; thus, the function autoloader will not be called again if the function is found in the global namespace.

Example “PSR-4-style” (except the last part of the namespace is the file it is in) function autoloader:

<?php
 
spl_autoload_register(function ($function) {
    $function_path = dirname(str_replace('\\', DIRECTORY_SEPARATOR, $function));
    $file = __DIR__ . '/functions/' . $function_path . '.php';
 
    if (file_exists($file)) {
        require_once $file;
    }
}, false, false, SPL_AUTOLOAD_FUNCTION);

Function autoloading doesn’t appear to have a significant impact on performance; however, the function autoloader itself (depending upon its implementation) may have a performance impact.

To help mitigate any potential performance impact of function autoloading many unqualified functions, a function will only be searched for once per namespace.

The spl_autoload function will not be modified. It may be used as a function autoloader if the programmer desires, though it will limit the programmer to a single function per file.

spl_autoload_unregister will be updated to accept the new constants as the second parameter to unregister an autoloader from either mode.

spl_autoload_functions will be updated to accept one of the new constants as the first parameter. Passing both (i.e., SPL_AUTOLOAD_CLASS | SPL_AUTOLOAD_FUNCTION) will result in all registered functions.

The spl_autoload_call function will be modified to accept a second parameter of one or both of the constants, with the default value set to SPL_AUTOLOAD_CLASS. The name of the first parameter will be changed to $name to reflect that it can be a class or function name.

In the event that both constants are passed, it will attempt to autoload both types.

spl_autoload_call('Some\func', SPL_AUTOLOAD_FUNCTION); // Calls the function autoloader
spl_autoload_call('Some\func'); // Calls the class autoloader
spl_autoload_call('Some\func', SPL_AUTOLOAD_CLASS); // Calls the class autoloader
spl_autoload_call('func', SPL_AUTOLOAD_FUNCTION | SPL_AUTOLOAD_CLASS); // Calls both autoloaders with the name 'func'

The function_exists function will be updated to include a boolean option ($autoload) as the second parameter, which will default to true. If set to true, the function autoloader will be called if the function is not defined, otherwise, it will not be called.

There shouldn’t be any backward incompatible changes.

8.5 or later.

• Potential changes to JIT helpers to call the autoloader instead of reading from the function table directly.

Two new constants will be added to the SPL extension: SPL_AUTOLOAD_CLASS, SPL_AUTOLOAD_FUNCTION.

None.

Potentially, constants and stream wrappers can be added in a similar fashion.

As per the voting RFC a yes/no vote with a 2/3 majority is needed for this proposal to be accepted.

Voting started on 2023-XX-XX and will end on 2023-XX-XX.

Review the implementation on GitHub #15471

• Implentation: PR #15471
• Version: TBD
• PHP Manual Entry: TODO

• autofunc: This heavily influenced this RFC. (declined in 2011)
• function_autoloading: This RFC was declined in 2011.
• function_autoloading_v2: This RFC was declined in 2012.

Thank you for all of those that contributed to the discussions back then. I hope that this RFC will be successful.

Autoloading of other types such as constants and stream wrappers will come in a later RFC.