Online PHP editor | output for U0J5m

<?php var_dump(php_uname('s')); $base_dir = sys_get_temp_dir() . DIRECTORY_SEPARATOR; file_put_contents($base_dir . 'Baz.php', "<?php namespace Foo\Bar; class BAZ {}"); file_put_contents($base_dir . 'Buz.php', "<?php namespace Foo\Bar; class Buz {}"); spl_autoload_register(function ($class) { echo "Trying to autoload $class\n"; // project-specific namespace prefix $prefix = 'Foo\\Bar\\'; // base directory for the namespace prefix global $base_dir; # = __DIR__ . '/src/'; // does the class use the namespace prefix? $len = strlen($prefix); if (strncmp($prefix, $class, $len) !== 0) { // no, move to the next registered autoloader return; } // get the relative class name $relative_class = substr($class, $len); // replace the namespace prefix with the base directory, replace namespace // separators with directory separators in the relative class name, append // with .php $file = $base_dir . str_replace('\\', '/', $relative_class) . '.php'; // if the file exists, require it if (file_exists($file)) { require $file; } else { echo "Could not require $file\n"; } }); // This works as expected because the class name matches the intended // case in the file and as it is represented on disk. $c1 = new \Foo\Bar\Baz(); // This works because PHP is PHP. This is not even going to hit the // PSR-4 autoloader. The *usage* of this classname by the user is not // PSR-4 compliant but that does not make the *autoloader* noncompliant. $c2 = new \Foo\Bar\BAZ(); var_dump($c1 == $c2); // This is going to be rejected by the PSR-4 autoloader implementation. // That is fine *and expected* because the *usage* of the classname by // the user is incorrect. // // On some platforms this may actually work but that is a byproduct of // certain platforms not caring about case. But again, the *usage* of // this classname *in this context* is not PSR-4 compliant. // // PSR-4 says that case is important and that case MUST be taken into // account when creating the file path representing the class name. It // also dictates that case MUST be taken into account when you create // files on disk for the FQCN in question. // // If the FQCN is \Foo\Bar\Baz in src/Baz.php, then specifying the class // with any other case than \Foo\Bar\Baz by the user is not compliant // with PSR-4. This is a problem with the user using the wrong classname // and the user should not expect this to work if they are following // the documented case for the classes in question. // // In some cases the planets will align and allow this to work anyway. // For instance, I think if you ran this on Windows it would actually // work. // // All the autoloader implementation can do is *try* to ensure it is // using the right case. If PHP / the platform discards that information // it is out of scope of PSR-4. $c3 = new \Foo\Bar\BUZ(); $c4 = new \Foo\Bar\Buz(); var_dump($c3 == $c4); // In the end, the fact that PHP considers \Foo\Bar\Buz and \Foo\Bar\BUZ // to be the same complicates things. This detail was ignored by PSR-0 // and it was one of the big things that people considered "bad" about it. // // The intent with PSR-4 is to ensure that people do not rely on the fact // that PHP is fuzzy in its handling of case for classnames and namespaces // and ensure that everyone uses the same case in all contexts for the // same class. // // There ARE edge cases where PHP will allow things that it shoudln't, but // PSR-4 autoloader implementations only need care about ensuring that it // locates and loads files using the case for the classname given it. As // long as this is the case, anything else PHP does weird is out of scope // for PSR-4 autoloader implementations.