README

Intro

PHP lacks generics and therefore a user-land library such as this can be a useful reusable base implementation to provide concepts such as an immutable set. In paradigms such as Functional Programming or Domain Driven Design, immutability is an essential component to encapsulate the state of your objects.

Quickstart

composer require identity-layer/collection

<?php

declare(strict_types=1);

use IdentityLayer\Collection\Exception\InvalidTypeException;
use IdentityLayer\Collection\ImmutableSet;

/**
 * Class UserCollection
 * @method static UserCollection fromArray(User[] $user)
 */
class UserCollection extends ImmutableSet
{
    public static function T(): string
    {
        return User::class;
    }

    public static function itemsEqual(object $item1, object $item2): bool
    {
        if (!$item1 instanceof User || !$item2 instanceof User) {
            throw new InvalidTypeException(
                sprintf('Both comparators must be of type %s', User::class)
            );
        }

        return $item1->equals($item2);
    }
}

Examples

Initialise Collection

$users = UserCollection::fromArray([
    new User('Joe Bloggs'),
    new User('Jane Doe'),
    new User('John Smith'),
]);

Iterate collection

/** @var User $user */
foreach ($users as $user) {
    echo $user->firstname();
}

This example shows how we can iterate using a foreach loop over each item in the collection.

Comparing sets

$set1 = NumberCollection::fromArray([
    new Number(3),
    new Number(1),
    new Number(2),
]);

$set2 = NumberCollection::fromArray([
    new Number(1),
    new Number(2),
    new Number(3),
    new Number(3),
]);

$set1->equals($set2); // true

Note that the order items are added makes no difference. Duplicate items will simply be removed from the collection automatically and these will not effect any comparison either.

Map

Map through the collection to produce a new collection of the same type:

$numbers = NumberCollection::fromArray([
    new Number(1),
    new Number(2),
    new Number(3),
]);

$squaredNumbers = $numbers->map(function (Number $number) {
    return new Number($number->pow(2));
});

$numbers; // 1, 4, 9

In this example we square a collection of numbers and return the resulting collection. A new collection will be returned. It works in much the same way the array_map function does except it does not return an array.

Reduce

$numbers = NumberCollection::fromArray([
    new Number(3),
    new Number(1),
    new Number(2),
]);

$numbersAdded = $numbers->reduce(function ($carry, Number $number) {
    $carry += $number->value();
    return $carry;
}));

$numbersAdded; // 6

Filter

$fruits = FruitCollection::fromArray([
    new Fruit('apple'),
    new Fruit('orange'),
    new Fruit('pear'),
    new Fruit('banana'),
    new Fruit('kiwi'),
    new Fruit('mango'),
    new Fruit('plum'),
]);

$filteredFruit = $fruits->filter(function (ValueObject $fruit) {
    return strlen($fruit->getValue()) <= 4;
});

$filteredFruit; // pear, kiwi, plum

In this example we return a new collection filtered using the callback provided. It works much the same as the array_filter function built into PHP but returns a new collection of the same type instead of an array.

identity-layer / collection

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