Collections with PHP 5.5 Generators

collection-with-generators.php

<?php
// PoC for collection pipeleines with improved memory footprint

// requires php 5.5 >= 5.5.24
// or       php 5.6 >= 5.6.8
// or       php 7
//
// see: https://bugs.php.net/bug.php?id=69221

class Collection extends \IteratorIterator {
    public static function fromArray(array $array)
    {
        return new static(new \ArrayIterator($array));
    }
    public static function fromGenerator(callable $callback)
    {
        $generator = $callback();
        if (! $generator instanceof \Generator) {
            throw new \InvalidArgumentException('Callback did not return a generator');
        }
        return new static($generator);
    }
    public function filter(callable $callback)
    {
        return self::fromGenerator(function() use ($callback) {
            foreach ($this->getInnerIterator() as $key => $value) {
                if ($callback($value, $key)) {
                    yield $key => $value;
                }
            }
        });
    }
    public function map(callable $callback)
    {
        return self::fromGenerator(function() use ($callback) {
            foreach ($this->getInnerIterator() as $key => $value) {
                yield $key => $callback($value);
            }
        });
    }
    public function each(callable $callback)
    {
        foreach ($this->getInnerIterator() as $key => $value) {
            $callback($value, $key);
        }
    }
}