https://medium.com/p/7b31f025ab6a - with autoloading

index.php

<?php

function autoload_src($file): bool
{
    echo sprintf('autoload_src: Looking for "%s".%s', $file, PHP_EOL);

    if (strtolower(($extract = explode('\\', $file))[0]) === 'source') {
        return loadFileIfExists('./src', $extract[1] ?? '');
    }

    return false;
}

function autoload_app($file): bool
{
    echo sprintf('autoload_app: looking for "%s".%s', $file, PHP_EOL);

    if (strtolower(($extract = explode('\\', $file))[0]) === 'app') {
        return loadFileIfExists('./app', $extract[1] ?? '');
    }

    return false;
}

function autoload_current($file): bool
{
    echo sprintf('autoload_current: looking for "%s".%s', $file, PHP_EOL);

    return loadFileIfExists('.', $file);
}

function loadFileIfExists(string $directory, string $filename): bool
{
    if (file_exists($path = sprintf('%s/%s.php', rtrim($directory, '/'), $filename))) {
        include($path);

        return true;
    }

    return false;
}

spl_autoload_register('autoload_app');
spl_autoload_register('autoload_src');
spl_autoload_register('autoload_current', prepend: true);

echo sprintf('autoloader order: %s.%s', json_encode(spl_autoload_functions()), PHP_EOL);
//spl_autoload_unregister('autoload_two');
//var_dump(spl_autoload_functions());

echo (new Current())->sayHello('anik');