Request for Comments: Namespace Issues and Greg's Solutions

• Version: 1.0
• Date: 2008-10-15
• Author: Greg Beaver cellog@php.net
• Status: Under Discussion
• First Published at: http://wiki.php.net/rfc/namespaceissues

This RFC discusses issues with the current namespace implementation in PHP, and Greg's proposed solutions

Namespaces are mostly working, but there are a few issues to be resolved. A short list:

1. conflict between namespaced functions and static class methods
2. resolving access to internal classes

Contrary to the doom and gloom on php-internals, there is no technical barrier to implementing namespaces properly. There is, however, a substantial political barrier. The internals developers who are namespace experts do not agree on the priorities for namespaces, and this is the only reason nothing has been committed. I strongly disagree with the contention that namespaces are flawed. One need only use them to see that they work just fine, except for a few rare edge cases.

My interest in this document is simply to point out the only remaining issues and how easy it is to solve them. None of the other solutions proposed (such as re-using -> for staticclass->method()) will work. Let's be clear: the solutions for problem #1 I am mentioning here are the *only* way to solve the problems that will be manageable and safe. The solution I mention for problem #2 is also the only way to safely solve the problem, although it does introduce some extra work to use internal classes.

The first file “foo.php”:

<?php
namespace one::step;
function two(){}
 
namespace one;
class step {
static function two(){}
}
?>

The second file “main.php”:

include 'foo.php';
// is this class one::step or namespace one::step?
one::step::two();

There are 4 easy ways to solve this problem

1. use ::: as primary namespace separator
2. use a different separator between namespace name and element such as one::step:::two() or one:::step::two()
3. explicit disambiguation using "use namespace blah::blah;/use class blah::blah;"

<?php
include 'foo.php';
use namespace one::step;
// this is now namespace one::step, function two
one::step::two();

   If the "use" statement is missing, an E_WARNING should also be thrown to alert the user to the ambiguity
4. disallow mixing namespaces and classes with the same name

I prefer #2, but would be happy with #3 or #1.

1. ambiguity is resolved

1. all existing namespace code must be rewritten with extra : added to all ::
2. ::: is visually similar to :: so this:::example:::with::slight:::error:::is:::hard:::to::see();

1. ambiguity is resolved
2. less chance for visual error (con #2 above)  this::example::with:::slight::error::is::easier:::to::see();

1. requires new paradigm, a separator between namespace and element name, something no other language does.
2. all namespaced code would need to be modified with this difference.
3. ::name would probably need to be changed to :::name for consistency.

1. no changes need be made to existing syntax
2. ambiguity is resolved with a single line of code
3. a clear warning is issued when ambiguity exists
4. execution never halts on ambiguity

1. blah::blah(); would trigger autoload in the ambiguity detection, so code that mixes __autoload() with namespaced functions
   could experience a performance slowdown.

1. no changes need be made to existing syntax
2. ambiguity is resolved by fatal error - very clear.

1. namespaces and classes cannot have the same name, a common practice with Underscored_Class_Names
2. in autoloaded code, the error would almost always be at runtime, making debugging difficult

Currently, PHP resolves this code as follows:

blah.php:

namespace blah;
function __autoload($class)
{
    include $class . '.php';
}
$a = new Exception('hi');

1. if blah::Exception exists, use it 2. if internal class Exception exists, use it 3. try to autoload blah::Exception

Thus, $a will be an object of class “Exception” even if blah::Exception exists in “Exception.php” as it will never be autoloaded. However, if this file were executed:

namespace blah;
class Exception {}
include 'blah.php';

$a would be an object of class “blah::Exception”.

The solution is to change the resolution order to:

1. if blah::Exception exists, use it 2. try to autoload blah::Exception 3. if internal class Exception exists, use it

This has the advantage that the above examples will always run the same way, instantiating “blah::Exception.” The only drawback is that for true internal classes, autoload() would still be called, as in the following example.

This will introduce an autoload for RecursiveIteratorIterator and RecursiveDirectoryIterator in this script:

autoload.php:

<?php
function __autoload($class) {include $class . '.php';}
?>

<?php
namespace blah;
include 'autoload.php';
$a = new RecursiveIteratorIterator(new RecursiveDirectoryIterator('.'));
?>

but fortunately it can be easily fixed via a use statement:

<?php
namespace blah;
use ::RecursiveIteratorIterator,::RecursiveDirectoryIterator;
include 'autoload.php';
$a = new RecursiveIteratorIterator(new RecursiveDirectoryIterator('.'));

This will be better for 99% of scripts, as evidenced by the ratio of internal vs. userspace classes (see http://marc.info/?l=php-internals&m=122127176407546&w=2 for detail)