Building Custom Collections

Custom collections encapsulate item rules and expose iteration or counting interfaces.

What It Does

Custom collections encapsulate item rules and expose iteration or counting interfaces. The following examples distinguish a normal use case, a boundary case and a practical application.

Requirements and Compatibility

PHP 8.x and a local test environment. Apply input validation, correct error handling and the requirements of any optional libraries.

The code focuses on the core concept. Production implementation may also need routes, validation, persistence, authorization or deployment tooling.

Example 1: Basic Behavior

Understand the primary operation and its inputs.

<?php
final class IdCollection implements IteratorAggregate { public function __construct(private array $ids) {} public function getIterator(): Traversable { return new ArrayIterator($this->ids); } }
foreach (new IdCollection([1, 3, 5]) as $id) echo $id;

Example 2: Another Case

Check failure behavior or a different execution path.

<?php
final class ProductList implements Countable { public function __construct(private array $items) {} public function count(): int { return count($this->items); } }
echo count(new ProductList(['A', 'B']));

Practical Example: Putting It to Use

Apply the behavior in a small, controlled scenario.

<?php
final class UniqueValues { private array $values = []; public function add(string $value): void { $this->values[$value] = true; } public function all(): array { return array_keys($this->values); } }
$set = new UniqueValues(); $set->add('a'); $set->add('a'); print_r($set->all());

Important Behavior and Edge Cases

Define whether values are unique, ordered or mutable instead of mimicking arrays accidentally.

Comparison with Related Functions or Approaches

Common Beginner Mistakes

Key Takeaways

• Custom collections encapsulate item rules and expose iteration or counting interfaces.
• Define whether values are unique, ordered or mutable instead of mimicking arrays accidentally.
• IteratorAggregate and Countable support native foreach and count().

Before adapting these examples, verify the return values, test the failure paths and confirm that your application meets its security and environment requirements.