Q:

PHP PSR-0 + several namespaces in one file and autoload

I've been thinking for a while about defining several namespaces in one php file and so, having several classes inside this file.
Suppose, I want to implement something like Doctrine\ORM\Query\Expr:
Expr.php
Expr
|-- Andx.php
|-- Base.php
|-- Comparison.php
|-- Composite.php
|-- From.php
|-- Func.php
|-- GroupBy.php
|-- Join.php
|-- Literal.php
|-- Math.php
|-- OrderBy.php
|-- Orx.php
`-- Select.php

It would be nice if I had all of this in one file - Expr.php:
namespace Doctrine\ORM\Query;
class Expr {
    // code
}

namespace Doctrine\ORM\Query\Expr;

class Func {
    // code
}

// etc...

What I'm thinking of is directories naming convention and, unlike PSR-0 having several classes and namespaces in one file. It's best explained by the code:
ls Doctrine/orm/query
Expr.php

that's it - only Expr.php
Since Expr.php is somewhat I call a "meta-namespace" for Expr\Func, it make sense to place all the classes inside Expr.php (as shown above).
So, the vendor name is still starts with an uppercased letter (Doctrine) and the other parts of namespace start with lowercased letter. We can write an autoload so it would respect this notion:
function load_class($class) {
    if (class_exists($class)) {
        return true;
    }
    $tokenized_path = explode(array("_", "\\"), DIRECTORY_SEPARATOR, $class);
    // array('Doctrine', 'orm', 'query', 'Expr', 'Func');
    //                                    ^^^^
    // first, we are looking for first uppercased namespace part
    // and if it's not last (not the class name), we use it as a filename 
    // and wiping away the rest to compose a path to a file we need to include
    if (FALSE !== ($meta_class_index = find_meta_class($tokenized_path))) {
        $new_tokenized_path = array_slice($tokenized_path, 0, $meta_class_index);
        $path_to_class = implode(DIRECTORY_SEPARATOR, $new_tokenized_path);
    }
    else { // no meta class found
        $path_to_class = implode(DIRECTORY_SEPARATOR, $tokenized_path);
    }
    if (file_exists($path_to_class.'.php')) {
        require_once $path_to_class.'.php';
    }
    return false;
}

Another reason to do so is to reduce a number of php files scattered among directories.
Usually you check file existence before you require a file to fail gracefully:
file_exists($path_to_class.'.php');

If you take a look at actual Doctrine\ORM\Query\Expr code, you'll see they use all of the "inner-classes", so you actually do:
file_exists("/path/to/Doctrine/ORM/Query/Expr.php");
file_exists("/path/to/Doctrine/ORM/Query/Expr/AndX.php");
file_exists("/path/to/Doctrine/ORM/Query/Expr/Base.php");
file_exists("/path/to/Doctrine/ORM/Query/Expr/Comparison.php");
file_exists("/path/to/Doctrine/ORM/Query/Expr/Composite.php");
file_exists("/path/to/Doctrine/ORM/Query/Expr/From.php");
file_exists("/path/to/Doctrine/ORM/Query/Expr/Func.php");
file_exists("/path/to/Doctrine/ORM/Query/Expr/GroupBy.php");
file_exists("/path/to/Doctrine/ORM/Query/Expr/Join.php");
file_exists("/path/to/Doctrine/ORM/Query/Expr/Literal.php");
file_exists("/path/to/Doctrine/ORM/Query/Expr/Math.php");
file_exists("/path/to/Doctrine/ORM/Query/Expr/OrderBy.php");
file_exists("/path/to/Doctrine/ORM/Query/Expr/Orx.php");
file_exists("/path/to/Doctrine/ORM/Query/Expr/Select.php");

in your autoload which causes quite a few I/O reads.
Isn't it too much to check on each user's hit?
I'm just putting this on a discussion.
I want to hear from another PHP programmers what do they think of it.
And, of course, if you have a silver bullet addressing this problems I've designated here, please share.
I also have been thinking if my vogue question fits here and according to the FAQ it seems like this question addresses "software architecture" problem slash proposal.
I'm sorry if my scribble may seem a bit clunky :)
Thanks.

A:

Keep using a single file per class.
You use APC, right? If you don't, start doing it right now. APC will cache the opcode, thus there will be no performance hit on the file checking.
It's not worth losing so much readability.

