How can I tell whether a function returns “nothing” or NULL?

Question

Consider a function that explicitly returns null :

function nullreturn() {return null;}
$rv = nullreturn();
var_dump($rv);
var_dump(isset($rv));
var_dump(is_null($rv));

Which identifies as null -- as expected.

NULL
bool(false)
bool(true)

And consider a function with no return value -- or even a return statement:

function noreturn() {}
$rv = noreturn();
var_dump($rv);
var_dump(isset($rv));
var_dump(is_null($rv));

Which also identifies as null :

NULL
bool(false)
bool(true)

... is there a way to determine that noreturn returns "nothing" instead of null ?

---

^{As to why I need this null / void distinction, I've just been trying to achieve compatibility with a previous service implementation that did make this distinction and which includes tests for it. But, it's probably not critical. I just don't want to strip away the relevant tests and hope I wasn't depending on the distinction if I were overlooking an achievable solution .}

Answer 1

No. Not returning, and returning NULL , are the exact same thing. A function with no return value implicitly returns NULL . This applies in many languages. Sorry if this isn't the answer you're looking for, but it is reality.

The following each do the exact same thing:

function A() {
    return;
}

function B() {
    return NULL;
}

function C() {
}

See also return in the PHP manual :

Note: If no parameter is supplied, then the parentheses must be omitted and NULL will be returned. Calling return with parentheses but with no arguments will result in a parse error.