Legacy PHP4 behavior is still there in current PHP versions. Could lead to debug nightmare.

class Test
{
	public function test()
	{
		echo 'Hello!';
		// it could be less innocent i.e. format disk ;)
	}
}

$test = new Test();

// runs Test::test()

$fact = function($n) use (&$fact) {
	if ($n === 1) {
        return 1;
    }
 
    return $fact($n - 1) * $n;
};
echo $fact(5); // =120

Very useful in case when foreign constraints aren't working.

SELECT TABLE_NAME
FROM information_schema.TABLES
WHERE TABLE_SCHEMA='my_db_name'
AND TABLE_TYPE='BASE TABLE'
AND ENGINE IN ('MARIA','MyISAM')

Sometimes you don't want to spoil API in order to test private or protected method of a class.

A good example is a public method that calls one of two private methods depending on the presence of PECL extension. Running tests twice with different PHP configuration is a waste of time. Making methods public isn't good for API.

function callPrivateMethod($object, $method, $args)
{
    $classReflection = new \ReflectionClass(get_class($object));
    $methodReflection = $classReflection->getMethod($method);
    $methodReflection->setAccessible(true);
    $result = $methodReflection->invokeArgs($object, $args);
    $methodReflection->setAccessible(false);
    return $result;
}

$myObject = new MyClass();
callPrivateMethod($myObject, 'hello', ['world']);

The code determines number of significant lines in the code. It skips newlines and comments. The plan is to skip doc-comments as well.

Can you improve it? Make it simpler and faster? Send your revisions. I think mine is the simplest one.

public function valid_length($code) {
	$count = 0;
	foreach (explode("\n", $code) as $line) {
		$line = trim($line);
		$line !== '' &&
		$line !== '{' &&
		$line !== '}' &&
		preg_match_all('~(?://|[#])~', $line) !== 1 ? $count ++ : false;
	}

	if ($count > 18) {
		$this->form_validation->set_message('valid_length', 'Your stash has more than 18 lines');

		return false;
	} else {
		return true;
	}
}

Most probably PHP 7 is going to have anonymous classes. Above is my use case for these. What are yours?

Would be glad to receive some ideas as revisions.

$image = new class {
	public width  = null;
	public height = null;

	public function __construct($filename) {
		list($width, $height) = getimagesize($filename);

		$this->width  = $width;
		$this->height = $height;
	}

	public function resize($width, $height) {
		// some code
	}
};

$image->resize(500, 500);

In C++, C# etc. you know what will be returned from a method. No surprises such as getting a string instead of expected int.

Using PHP 7 you can finally specify return type!

class Post extends CI_Model {

	public function __construct() {
		$this->load->database();
		$this->load->helper(['url', 'date']);
	}

	/**
	 * Getting post by ID
	 * @param $id
	 * @return array
	 */
	public function get_post_by_id($id): array {
		$query = $this->db->where('id', $id)->get('post');
		return ! is_null($query->row()) ? $query->row() : [];
	}
}

I've been searching for a good way to form a tree. I think this one is ideal. Can you make it better?

private function buildTree($data)
{
	$tree       = [];
	$references = [];

	foreach ($data as $id => &$node) {
		$references[$node['id']] = &$node;
		$node['children'] = [];

		if (is_null($node['parent_id'])) {
			$tree[] = &$node;
		} else {
			$references[$node['parent_id']]['children'][] = &$node;
		}
	}

	return $tree;
}