Collections

collections.php

<?php

final class User
{
    private $name;

    public function __construct(string $name)
    {
        $this->name = $name;
    }

    public function getName(): string
    {
        return $this->name;
    }
}

class Collection extends IteratorIterator
{
    public function take(int $n): Collection
    {
        return new static(new LimitIterator($this, 0, $n));
    }

    public function filter(callable $f): Collection
    {
        return new static(new CallbackFilterIterator($this, $f));
    }

    public function get(): array
    {
        return iterator_to_array($this);
    }
}

final class UsersCollection extends Collection
{
    public function __construct(Traversable $traversable)
    {
        // Can't make the constructor private :[
        parent::__construct($traversable);
    }

    public static function safe(User ...$users)
    {
        return new self(new ArrayIterator($users));
    }

    public static function unsafe(Traversable $traversable)
    {
        return new self($traversable);
    }

    public function current(): User
    {
        return parent::current();
    }
}

/**
 * Example 1 shows how to do lazy stuff
 */
function example1()
{
    $users = UsersCollection::unsafe((function () {
        while (true) {
            yield new User(str_shuffle('ABCDEFGH'));
        }
    })());

    $filter = function (User $user) {
        return $user->getName()[0] == 'H';
    };

    $view = $users->filter($filter)->take(10);

    echo get_class($view) . PHP_EOL;

    foreach ($view as $user) {
        echo $user->getName() . PHP_EOL;
    }
}

/**
 * Example 2 shows how to do eager stuff
 */
function example2()
{
    $users = UsersCollection::safe(new User('Foo'), new User('Bar'), new User('Baz'));

    foreach ($users->take(2) as $user) {
        echo $user->getName() . PHP_EOL;
    }
}

/**
 * Retrieving the underlying array.
 */
function example3()
{
    $users = UsersCollection::unsafe((function () {
        while (true) {
            yield new User(str_shuffle('ABCDEFGH'));
        }
    })());

    $ten = $users->take(10)->get();

    $transformed = UsersCollection::safe(...array_map(function (User $user): User {
        return new User("Good guy " . $user->getName());
    }, $ten));

    foreach ($transformed as $name) {
        echo $name->getName() . PHP_EOL;
    }
}

echo "Example 1: eager loading\n";
example1();

echo "\nExample 2: lazy loading\n";
example2();

echo "\nExample 3: delegate map functions and the like\n";
example3();

output.txt

Example 1: eager loading
UsersCollection
HBCFGAED
HEGBDCFA
HBFGCDEA
HBFCGADE
HDGEABCF
HFGCDABE
HBCEGFDA
HEADBCGF
HGCFDEBA
HFCDGEBA

Example 2: lazy loading
Foo
Bar

Example 3: delegate map functions and the like
Good guy BDEGHCFA
Good guy BEFCGHDA
Good guy ABCEGHDF
Good guy EBCGAHDF
Good guy FEHDCAGB
Good guy CAFBHEGD
Good guy AEFHGDCB
Good guy DCHFAEGB
Good guy FABGCEHD
Good guy CEHFDGAB