How to check if variable is array?... or something array-like

Question

I want to use a foreach loop with a variable, but this variable can be many different types, NULL for example.

So before foreach I test it:

if(is_array($var)){
  foreach($var as ...

But I realized that it can also be a class that implements Iterator interface. Maybe I am blind but how to check whether the class implements interface? Is there something like is_a function or inherits operator? I found class_implements, I can use it, but maybe there is something simpler?

And second, more important, I suppose this function exist, would be enough to check if the variable is_array or "implements Iterator interface" or should I test for something more?

Answer 1

If you are using foreach inside a function and you are expecting an array or a Traversable object you can type hint that function with:

function myFunction(array $a)
function myFunction(Traversable)

If you are not using foreach inside a function or you are expecting both you can simply use this construct to check if you can iterate over the variable:

if (is_array($a) or ($a instanceof Traversable))

Answer 2

foreach can handle arrays and objects. You can check this with:

$can_foreach = is_array($var) || is_object($var);
if ($can_foreach) {
    foreach ($var as ...
}

You don't need to specifically check for Traversable as others have hinted it in their answers, because all objects - like all arrays - are traversable in PHP.

More technically:

foreach works with all kinds of traversables, i.e. with arrays, with plain objects (where the accessible properties are traversed) and Traversable objects (or rather objects that define the internal get_iterator handler).

(source)

Simply said in common PHP programming, whenever a variable is

• an array
• an object

and is not

• NULL
• a resource
• a scalar

you can use foreach on it.

Answer 3

You can check instance of Traversable with a simple function. This would work for all this of Iterator because Iterator extends Traversable

function canLoop($mixed) {
    return is_array($mixed) || $mixed instanceof Traversable ? true : false;
}