switch statement without break

Question

How come a case option in a switch statement that does not contain a break automatically forwards to a next case without check?

try {
    switch($param) {
        case "created":
            if(!($value instanceof \DateTime))
                throw new \Exception("\DateTime expected, ".gettype($value)." given for self::$param");
        case "Creator":
            if(!($value instanceof \Base\User)) {
                throw new \Exception(get_class($value)." given. \Base\User expected for self::\$Creator");                  
            }
        default:
            $this->$param = $value;
            break;
    }
} catch(Exception $e) {
    echo $e->getMessage();
}

If the param is "created" it will do the check in the created-case, which is good. When the check is succesful, I want the code to continue to the default option, that's why there is no break;. But instead it continues to "Creator" while $param != "Creator"!

I do know how to solve this (just add the default code in my case "created"), but I don't like to repeat that code too often. My actual question is: Why does it continue with the "Creator" case while the case is not "Creator".

Answer 1

Fallthrough was an intentional design feature for allowing code like:

switch ($command) {
  case "exit":
  case "quit":
    quit();
    break;
  case "reset":
    stop();
  case "start":
    start();
    break;
}

It's designed so that execution runs down from case to case.

default is a case like any other, except that jumping there happens if no other case was triggered. It is not by any means a "do this after running the actual selected case" instruction. In your example, you could consider:

  switch($param) {
    case "created":
        if(!($value instanceof \DateTime))
            throw new \Exception("\DateTime expected, ".gettype($value)." given for self::$param");
        break;
    case "Creator":
        if(!($value instanceof \Base\User)) {
            throw new \Exception(get_class($value)." given. \Base\User expected for self::\$Creator");                  
        }
        break;
}

$this->$param = $value;

The rule of thumb here is, if it doesn't depend on the switch, move it out of the switch.