Do these 3 things before closing this tab:
1Clear out junk files and repair common Windows errors2Scan for outdated or missing drivers - takes under a minute3Repair Windows errors before they cause bigger problemsPHP can iterate over objects with foreach. An ordinary object exposes its visible properties by default; to define a deliberate iterable interface, implement IteratorAggregate for an existing collection or Iterator when you need to control iteration state and movement.
How does foreach iterate over an object?
Use the same foreach syntax you use for arrays:
<?php
$book = new stdClass();
$book->title = 'The Pragmatic Programmer';
$book->author = 'Andrew Hunt';
foreach ($book as $key => $value) {
echo "$key: $valuen";
}
Because $book has no custom iterator, PHP traverses its visible properties. The PHP manual describes the default as: “By default, all visible properties will be used for the iteration.” See PHP object iteration and the foreach manual.
This default is convenient for simple objects, but it is not necessarily a collection API. A class’s properties may represent implementation details rather than values callers should loop through. Visibility also matters: iteration uses properties visible from the scope where the loop runs. If a class should expose a particular sequence, define that sequence explicitly with an iterator interface.
When should you use IteratorAggregate?
Use IteratorAggregate when the object already holds the data and should provide an iterable view of it. Its getIterator(): Traversable method returns an iterator or another traversable value; the interface is described by the PHP manual as an “Interface to create an external Iterator.” See IteratorAggregate.
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<?php
class BookCollection implements IteratorAggregate
{
public function __construct(private array $books)
{
}
public function getIterator(): Traversable
{
return new ArrayIterator($this->books);
}
}
$books = new BookCollection([
'clean-code' => 'Clean Code',
'refactoring' => 'Refactoring',
]);
foreach ($books as $key => $title) {
echo "$key: $titlen";
}
The collection keeps its backing array private while choosing what callers see during iteration. Returning an ArrayIterator is a compact option for array-backed data; the backing value in this example is an array. The ArrayIterator manual also flags a PHP 8.5 deprecation for using an object as its backing storage. Avoid new ArrayIterator($this) in new code; use an explicit array or a generator instead, and check the manual for the PHP version your project targets.
A generator is another concise way to expose values:
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public function getIterator(): Traversable
{
yield from $this->books;
}
Use yield from when the method can directly expose the stored iterable values and you do not need to construct a separate iterator object.
When should you implement Iterator?
Implement Iterator when the class itself needs to define how iteration is positioned, advanced, and read. The interface requires five methods: current(), key(), next(), rewind(), and valid(). See the Iterator interface manual.
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| Method | Purpose |
|---|---|
rewind() |
Initialize or reset the iteration position. |
valid() |
Report whether the current position contains an item. |
current() |
Return the value at the current position. |
key() |
Return the key for the current position. |
next() |
Advance to the next position. |
For example, this iterator walks an array while keeping its position in a separate integer:
<?php
class BookIterator implements Iterator
{
private int $position = 0;
public function __construct(private array $books)
{
}
public function current(): mixed
{
return $this->books[$this->position];
}
public function key(): mixed
{
return $this->position;
}
public function next(): void
{
++$this->position;
}
public function rewind(): void
{
$this->position = 0;
}
public function valid(): bool
{
return array_key_exists($this->position, $this->books);
}
}
$books = new BookIterator(['Clean Code', 'Refactoring']);
foreach ($books as $key => $title) {
echo "$key: $titlen";
}
foreach orchestrates the iterator methods: it resets the iterator, checks whether a position is valid, reads its key and value, then advances until no valid position remains. Here, valid() checks whether the position exists rather than whether its value is truthy. That distinction lets an iterator represent legitimate values such as false or null without mistaking them for the end of the sequence.
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Iterator vs. IteratorAggregate: which pattern fits?
| Need | Pattern | Why it fits |
|---|---|---|
| Loop over a plain object’s visible data | Default object iteration | It requires no interface, but properties visible in the calling scope become the iteration values. |
| Expose stored data with minimal iterator code | IteratorAggregate |
getIterator() returns an iterator or another Traversable value. |
| Define custom position and advancement behavior | Iterator |
The class implements all five methods governing state, access, and movement. |
In user-defined classes, implement Iterator or IteratorAggregate rather than trying to implement Traversable by itself. Traversable is a marker interface; it identifies traversable types but is not a standalone userland implementation target. Internal PHP classes can implement it directly. See the Traversable manual.
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Practical checks for a reliable iterator
- Expose only intended values. Prefer a deliberate iterator API over relying on all visible object properties when the class represents a collection.
- Keep validity separate from value. Decide whether a position exists independently of whether its value evaluates as true.
- Choose the simplest contract that fits. Use
IteratorAggregatefor stored data that can be returned as an existing iterable; useIteratorwhen custom state transitions are part of the design. - Check the runtime’s manual. Iterator behavior and deprecation guidance can be version-specific; in particular, consult the target PHP version before relying on
ArrayIteratorbacking behavior.
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