What is the logic behind is_iterable() when the variable is an empty object? What will the result be?

M66 2025-06-27

In PHP, is_iterable() is a function used to check whether a variable can be iterated over. This function returns true for arrays and objects that implement the Traversable interface; otherwise, it returns false. Many developers use is_iterable() in practical development to avoid type-related errors. However, when passing an empty object, the behavior of the is_iterable() function might be somewhat surprising. Next, we will examine this issue and see what result an empty object returns in is_iterable().

1. Basic Usage of is_iterable

First, let's understand the basic usage of the is_iterable() function. In PHP, is_iterable() checks whether a variable can be iterated over. For example, arrays and objects that implement the Traversable interface are considered iterable.

$myArray = [1, 2, 3];
$myObject = new ArrayObject([1, 2, 3]);
<p>echo is_iterable($myArray) ? 'true' : 'false';   // true<br>
echo is_iterable($myObject) ? 'true' : 'false';  // true<br>

As shown above, both arrays and objects implementing the Traversable interface return true.

2. What is an Empty Object?

An empty object usually refers to an object without properties or methods—that is, it contains no data or functionality. For example:

$emptyObject = new stdClass();

Here, $emptyObject is an empty object with no properties. Although it is an object, it doesn't have any actual data structures or methods. However, an empty object is still considered an instance of an object, which meets the basic definition of an object in PHP.

3. Behavior of an Empty Object in is_iterable()

Next, let's see what result we get when we pass an empty object to the is_iterable() function. Although an empty object itself has no properties or methods, it is still an object. According to the definition of is_iterable(), it does not directly check if an object is empty, but rather whether the object implements the Traversable interface.

$emptyObject = new stdClass();
echo is_iterable($emptyObject) ? 'true' : 'false';  // false

In this example, the empty object stdClass does not implement the Traversable interface, so is_iterable() returns false. This means that even if we pass an empty object, it will not be considered iterable.

4. Why Does an Empty Object Return false?

is_iterable() determines whether an object is iterable by checking if it implements the Traversable interface. In PHP, the stdClass class does not implement the Traversable interface; it is a plain class. Therefore, although it is an object, it lacks the capability to be iterated over, causing is_iterable() to return false.

If you want an object to be considered iterable, it must implement the Traversable interface, or more commonly implement the Iterator or IteratorAggregate interfaces. For example, ArrayObject implements the Traversable interface, so it is iterable even if it is empty.

$emptyObject = new ArrayObject();
echo is_iterable($emptyObject) ? 'true' : 'false';  // true

5. Conclusion

To summarize, when a variable is an empty object, the is_iterable() function returns false because empty objects like stdClass do not implement the Traversable interface. For an object to return true, it must implement that interface or be an array type. Therefore, when using is_iterable(), if you expect an empty object to pass the check, consider having the object implement the relevant interfaces or use an array instead of an object.

is_iterable