Vector using psalm.dev template annotations.

ImmutableVector.php

<?php

/**
 * @template T
 */
class ImmutableVector
{

    /**
     * @psalm-var T[]
     */
    private $items;

    /**
     * @psalm-param T[] $items
     */
    public function __construct(array $items)
    {
        $this->items = $items;
    }

    /**
     * @template R
     * @psalm-param callable(T):R $function
     * @psalm-return ImmutableVector<R>
     */
    public function map(callable $function): ImmutableVector
    {
        return new ImmutableVector(array_map($function, $this->items));
    }

    /**
     * @psalm-param callable(T):bool $function
     * @psalm-return ImmutableVector<T>
     */
    public function filter(callable $function): ImmutableVector
    {
        return new ImmutableVector(array_filter($this->items, $function));
    }

    /**
     * @pslam-param callable(T):void $function
     * @psalm-return ImmutableVector<T>
     */
    public function each(callable $function): self
    {
        foreach ($this->items as $item) {
            $function($item);
        }
        return $this;
    }

    /**
     * @template R
     * @psalm-param callable(R,T):R $function
     * @psalm-param R $start
     * @psalm-return R
     */
    public function reduce(callable $function, $start)
    {
        $tmp = $start;
        foreach ($this->items as $item) {
            $tmp = $function($tmp, $item);
        }
        return $tmp;
    }

    /**
     * @psalm-return ImmutableVector<T>
     */
    public function slice(int $from, int $to = -1): ImmutableVector
    {
        $index = 0;
        $a = [];
        foreach ($this->items as $item) {
            if ($index >= $from && ($index < $to || $to === -1)) {
                $a[] = $item;
            } elseif ($index >= $to && $to >= 0) {
                break;
            }
            $index++;
        }
        return new ImmutableVector($a);
    }

    /**
     * @psalm-return ImmutableVector<T>
     */
    public function take(int $amount): ImmutableVector
    {
        return $this->slice(0, $amount);
    }

    /**
     * @psalm-return ImmutableVector<T>
     */
    public function drop(int $amount): ImmutableVector
    {
        return $this->slice($amount);
    }

    /**
     * @psalm-return T[]
     */
    public function toArray(): array
    {
        return array_values($this->items);
    }
}