Crude, but tiny single-library PHP autoloading setups

crude_autoloading.php

<?php
// In the snippets below, you must replace '/path/to/lib' with the correct path.

// does not support namespaces with underscores
spl_autoload_register(function ($class) {
    $file = __DIR__ . '/path/to/lib/' . strtr(ltrim($class, '\\'), '_\\', '//') . '.php';
    is_readable($file) && (require $file);
});

// for a particular namespace
spl_autoload_register(function ($class) {
    $class = ltrim($class, '\\');
    if (0 !== strpos($class, 'NamespaceName\\')) {
        return;
    }
    $file = dirname(__DIR__) . '/path/to/lib/' . strtr($class, '_\\', '//') . '.php';
    is_readable($file) && (require $file);
});


// full PSR-0 compliant
spl_autoload_register(function ($class) {
    $classPaths = array(
        // class paths here...
    );
    $pieces = explode('\\', ltrim($class, '\\'));
    $pieces[count($pieces) - 1] = strtr($pieces[count($pieces) - 1], '_', '/');
    $relativePath = '/' . implode('/', $pieces) . '.php';
    foreach ($classPaths as $classPath) {
        if (is_readable($classPath . $relativePath)) {
            require $classPath . $relativePath;
            return;
        }
    }
});


// PSR-0 plus Zend Framework 1 support
set_include_path(get_include_path() . PATH_SEPARATOR . '/path/to/zf1/library');
spl_autoload_register(function ($class) {
    if (0 === strpos($class, 'Zend_')) {
        // We have to use require_once with a relative path, like ZF1 does. If not, PHP will
        // try to load the file twice.
        $relativePath = str_replace('_', '/', $class) . '.php';
        if (function_exists('stream_resolve_include_path')) {
            $resolvedPath = stream_resolve_include_path($relativePath);
            if ($resolvedPath && is_readable($resolvedPath)) {
                require_once $relativePath;
                return;
            }
        } else {
            // No way to check if path will resolve, let's just hope.
            require_once $relativePath;
            return;
        }
    }

    $classPaths = array(
        // class paths here...
    );
    $pieces = explode('\\', ltrim($class, '\\'));
    $pieces[count($pieces) - 1] = strtr($pieces[count($pieces) - 1], '_', '/');
    $relativePath = '/' . implode('/', $pieces) . '.php';
    foreach ($classPaths as $classPath) {
        if (is_readable($classPath . $relativePath)) {
            require $classPath . $relativePath;
            return;
        }
    }
});