IteratorAggregate interface in PHP - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to implement the IteratorAggregate interface in the class.

PHP

<?php
class MyCollection implements IteratorAggregate {
    private array $items = [];

    public function __construct(array $items) {
        $this->items = $items;
    }

    public function [1]() {
        return new ArrayIterator($this->items);
    }
}
?>

Drag options to blanks, or click blank then click option'

AgetItems

BfetchIterator

CgetIterator

Diterator

Attempts:

3 left

💡 Hint

Common Mistakes

Using a method name other than getIterator.

Not returning an iterator object.

The IteratorAggregate interface requires implementing the getIterator() method which returns an iterator.

2fill in blank

medium

Complete the code to return an iterator over the items array.

PHP

<?php
public function getIterator() {
    return new [1]($this->items);
}
?>

Drag options to blanks, or click blank then click option'

ATraversable

BIteratorAggregate

CIterator

DArrayIterator

Attempts:

3 left

💡 Hint

Common Mistakes

Using interface names instead of a concrete iterator class.

Returning the array directly instead of an iterator.

ArrayIterator is a built-in class that implements Iterator and can iterate over arrays.

3fill in blank

hard

Fix the error in the method signature to properly implement IteratorAggregate.

PHP

<?php
class Collection implements IteratorAggregate {
    public function [1](): Traversable {
        // method body
    }
}
?>

Drag options to blanks, or click blank then click option'

AgetIterator

Biterator

CgetItems

DfetchIterator

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect method names.

Omitting the return type declaration.

The method must be named getIterator and return a Traversable to satisfy the interface.

4fill in blank

hard

Fill both blanks to create a class that implements IteratorAggregate and returns an iterator over a private array.

PHP

<?php
class [1] implements IteratorAggregate {
    private array $data;

    public function __construct(array $data) {
        $this->data = $data;
    }

    public function getIterator(): [2] {
        return new ArrayIterator($this->data);
    }
}
?>

Drag options to blanks, or click blank then click option'

ADataCollection

BTraversable

CIterator

DArrayAccess

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect return types.

Choosing unrelated class names.

The class name can be any valid name like DataCollection. The getIterator method must return Traversable.

5fill in blank

hard

Fill all three blanks to create a class that implements IteratorAggregate, stores items, and returns an iterator.

PHP

<?php
class [1] implements IteratorAggregate {
    private array $[2];

    public function __construct(array $items) {
        $this->[2] = $items;
    }

    public function getIterator(): [3] {
        return new ArrayIterator($this->[2]);
    }
}
?>

Drag options to blanks, or click blank then click option'

AItemList

Bitems

CTraversable

Ddata

Attempts:

3 left

💡 Hint

Common Mistakes

Mismatching property names.

Incorrect return type for getIterator.

The class name is ItemList, the private property is items, and getIterator returns Traversable.

Practice

1.

What is the main purpose of the IteratorAggregate interface in PHP?

easy

A. To allow an object to be iterated with foreach by providing an external iterator.

B. To automatically sort arrays inside an object.

C. To enforce type checking on array elements.

D. To convert an object into a string representation.

Solution

1. Step 1: Understand the role of IteratorAggregate

   The interface requires implementing getIterator() which returns an iterator object.

2. Step 2: Connect to foreach usage

   This allows the object to be used in foreach loops by providing the iterator externally.

3. Final Answer:

   To allow an object to be iterated with foreach by providing an external iterator. -> Option A

4. Quick Check:

   IteratorAggregate enables foreach iteration [OK]

Hint: Remember: IteratorAggregate provides an iterator for foreach [OK]

Common Mistakes:

• Thinking it sorts data automatically
• Confusing it with string conversion
• Assuming it enforces type checks

2.

Which method must a class implement when it uses the IteratorAggregate interface?

easy

A. getItems()

B. iterate()

C. getIterator()

D. toArray()

Solution

1. Step 1: Recall interface requirements

   The IteratorAggregate interface requires the getIterator() method.

2. Step 2: Confirm method name

   This method must return an iterator object to enable iteration.

3. Final Answer:

   getIterator() -> Option C

4. Quick Check:

   IteratorAggregate requires getIterator() [OK]

Hint: Interface method is always getIterator() [OK]

Common Mistakes:

• Using iterate() instead of getIterator()
• Confusing with toArray() method
• Assuming getItems() is required

3.

What will be the output of this PHP code?

<?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 . ' ';
}

medium

A. ArrayIterator Object

B. 1 2 3

C. Error: getIterator must return array

D. No output

Solution

1. Step 1: Understand getIterator() return

   The method returns an ArrayIterator over the array [1, 2, 3].

2. Step 2: foreach loops over iterator

   The foreach loop iterates over the items 1, 2, and 3, echoing each with a space.

3. Final Answer:

   1 2 3 -> Option B

4. Quick Check:

   foreach prints each item from ArrayIterator [OK]

Hint: getIterator returns ArrayIterator to enable foreach [OK]

Common Mistakes:

• Expecting an error because getIterator returns ArrayIterator
• Thinking it prints object instead of values
• Missing the space after each number

4.

Identify the error in this PHP class implementing IteratorAggregate:

<?php
class Numbers implements IteratorAggregate {
    private array $nums = [10, 20, 30];
    public function getIterator() {
        return $this->nums;
    }
}

medium

A. getIterator() must return an object implementing Traversable, not an array.

B. Property $nums should be public, not private.

C. Class must implement Iterator, not IteratorAggregate.

D. getIterator() method must be static.

Solution

1. Step 1: Check getIterator() return type

   It returns an array, but getIterator() must return an object implementing Traversable.

2. Step 2: Understand interface contract

   Returning an array causes a type error because arrays do not implement Traversable.

3. Final Answer:

   getIterator() must return an object implementing Traversable, not an array. -> Option A

4. Quick Check:

   getIterator() returns Traversable object [OK]

Hint: getIterator must return Traversable object, not array [OK]

Common Mistakes:

• Returning array directly from getIterator()
• Thinking private properties cause error here
• Assuming getIterator() must be static

5.

You want to create a class FilteredCollection that implements IteratorAggregate and only iterates over items greater than 5 from an internal array. Which implementation of getIterator() is correct?

<?php
class FilteredCollection implements IteratorAggregate {
    private array $items;
    public function __construct(array $items) {
        $this->items = $items;
    }
    public function getIterator(): Traversable {
        // Which code below is correct?
    }
}

hard

A. return new ArrayIterator($this->items);

B. return new ArrayIterator(array_map(fn($v) => $v > 5, $this->items));

C. return $this->items;

D. return new ArrayIterator(array_filter($this->items, fn($v) => $v > 5));

Solution

1. Step 1: Filter items greater than 5

   Use array_filter with a callback to keep only values > 5.

2. Step 2: Return an ArrayIterator over filtered items

   Wrap filtered array in ArrayIterator to satisfy Traversable return type.

3. Final Answer:

   return new ArrayIterator(array_filter($this->items, fn($v) => $v > 5)); -> Option D

4. Quick Check:

   Filter then wrap in ArrayIterator [OK]

Hint: Filter array first, then return ArrayIterator [OK]

Common Mistakes:

• Returning unfiltered array directly
• Using array_map instead of array_filter
• Not wrapping result in an iterator object