php 62 lines · 8 steps

An immutable typed collection in PHP

A final PHP class wraps Product objects in an immutable, iterable, countable collection keyed by SKU.

Explained by highlit

Intermediate immutability value-objects iterators type-safety collections

1<?php
2 
3declare(strict_types=1);
4 
5namespace App\Collection;
6 
7use App\Entity\Product;
8use ArrayIterator;
9use Countable;
10use InvalidArgumentException;
11use IteratorAggregate;
12use Traversable;
13 
14final class ProductCollection implements IteratorAggregate, Countable
15{
16    private array $products = [];
17 
18    public function __construct(Product ...$products)
19    {
20        foreach ($products as $product) {
21            $this->products[$product->getSku()] = $product;
22        }
23    }
24 
25    public function add(Product $product): self
26    {
27        $clone = clone $this;
28        $clone->products[$product->getSku()] = $product;
29 
30        return $clone;
31    }
32 
33    public function get(string $sku): Product
34    {
35        return $this->products[$sku]
36            ?? throw new InvalidArgumentException("No product with SKU {$sku}.");
37    }
38 
39    public function filter(callable $predicate): self
40    {
41        return new self(...array_filter($this->products, $predicate));
42    }
43 
44    public function totalPrice(): int
45    {
46        return array_reduce(
47            $this->products,
48            static fn (int $carry, Product $p): int => $carry + $p->getPriceInCents(),
49            0,
50        );
51    }
52 
53    public function getIterator(): Traversable
54    {
55        return new ArrayIterator(array_values($this->products));
56    }
57 
58    public function count(): int
59    {
60        return count($this->products);
61    }
62}

01 / 01

STEP 01

Walkthrough

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Three takeaways

1Cloning before mutation keeps a collection immutable so shared references never surprise you.
2Implementing IteratorAggregate and Countable lets your class behave like a native array in loops and count().
3Keying entries by a domain identifier like SKU gives free deduplication and O(1) lookup.

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