IteratorAggregate interface in PHP - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of IteratorAggregate with simple array

What is the output of this PHP code using IteratorAggregate?

PHP

<?php
class MyCollection implements IteratorAggregate {
    private array $items = [1, 2, 3];
    public function getIterator(): Traversable {
        return new ArrayIterator($this->items);
    }
}
$collection = new MyCollection();
foreach ($collection as $item) {
    echo $item . ' ';
}

A 1 2 3

B ArrayIterator Object

C Error: getIterator must return an array

D 1,2,3

💡 Hint

Remember that IteratorAggregate requires getIterator() to return an iterator object.

The getIterator() method returns an ArrayIterator over the items array. The foreach loop iterates over these items and prints them separated by spaces.

❓ Predict Output

intermediate

Output when getIterator returns a generator

What will this PHP code output when using IteratorAggregate with a generator?

PHP

<?php
class GenCollection implements IteratorAggregate {
    public function getIterator(): Traversable {
        yield 10;
        yield 20;
        yield 30;
    }
}
$gen = new GenCollection();
foreach ($gen as $value) {
    echo $value . '-';
}

A 10-20-30-

B ArrayIterator Object

C Fatal error: getIterator must return an Iterator object

D 10 20 30

💡 Hint

Generators implement Traversable and can be returned by getIterator.

The getIterator method yields values 10, 20, and 30. The foreach prints each value followed by a dash.

🔧 Debug

advanced

Identify the error in IteratorAggregate implementation

What error will this PHP code produce?

PHP

<?php
class BadCollection implements IteratorAggregate {
    private array $data = [5, 6, 7];
    public function getIterator(): array {
        return $this->data;
    }
}
$bad = new BadCollection();
foreach ($bad as $item) {
    echo $item;
}

A Syntax error: missing semicolon

B Outputs: 567

C Fatal error: getIterator must return an instance of Traversable

D TypeError: Cannot convert array to string

💡 Hint

Check the return type of getIterator method.

The getIterator method must return an object implementing Traversable, not an array. Returning an array causes a fatal error.

📝 Syntax

advanced

Which option correctly implements IteratorAggregate?

Which of the following PHP code snippets correctly implements IteratorAggregate?

A class C implements IteratorAggregate { public function getIterator(): array { return [1,2]; } }

B class C implements IteratorAggregate { public function getIterator(): Traversable { return new ArrayIterator([1,2]); } }

C class C implements IteratorAggregate { public function getIterator(): Traversable { return [1,2]; } }

D class C implements IteratorAggregate { public function getIterator() { return [1,2]; } }

💡 Hint

getIterator must return Traversable, not array.

Only option B returns an object implementing Traversable (ArrayIterator). Options A, B, and D return arrays or lack return type, causing errors.

🚀 Application

expert

Count items using IteratorAggregate and Countable

Given this PHP class implementing IteratorAggregate and Countable, what is the output of the code?

PHP

<?php
class CountableCollection implements IteratorAggregate, Countable {
    private array $elements = ['a', 'b', 'c', 'd'];
    public function getIterator(): Traversable {
        return new ArrayIterator($this->elements);
    }
    public function count(): int {
        return count($this->elements);
    }
}
$col = new CountableCollection();
echo count($col) . ' ';
foreach ($col as $item) {
    echo $item;
}

A abcd 4

B Error: Countable not implemented correctly

C 4 ArrayIterator Object

D 4 abcd

💡 Hint

Countable interface allows count() to work on the object.

The count() method returns 4, the number of elements. The foreach prints each element in order.