How to infer type from generics

[nunomaduro]

In this example psalm.dev/r/6dbda66dde, I want the both TKey and TValue to be an int and not specific integers. How can I make this happen?

[psalm-github-bot]

I found these snippets:

https://psalm.dev/r/6dbda66dde

<?php 

/**
 * @template TKey of array-key
 * @template TValue
 */
class Collection {
    /**
     * @var array<TKey, TValue>
     */
    protected $items = [];
	
	/**
     * Create a new collection.
     *
     * @param  array<TKey, TValue>  $items
     * @return void
     */
    public function __construct($items)
    {
        $this->items = $items;
    }
	
    /**
     * Add an item to the collection.
     *
     * @param  TKey  $key
     * @param  TValue  $item
     * @return $this
     */
    public function add($key, $item)
    {
        $this->items[$key] = $item;

        return $this;
    }
}

(new Collection([1, 2]))->add(2, 3);

Psalm output (using commit 9222b24):

ERROR: InvalidArgument - 39:31 - Argument 1 of Collection::add expects 0|1, 2 provided

ERROR: InvalidArgument - 39:34 - Argument 2 of Collection::add expects 1|2, 3 provided

[weirdan]

Inference has its limits, and there are time when you need to specify the type manually, e.g. https://psalm.dev/r/3b5cc796c1

[psalm-github-bot]

I found these snippets:

https://psalm.dev/r/3b5cc796c1

<?php 

/**
 * @template TKey of array-key
 * @template TValue
 */
class Collection {
    /**
     * @var array<TKey, TValue>
     */
    protected $items = [];
	
	/**
     * Create a new collection.
     *
     * @param  array<TKey, TValue>  $items
     * @return void
     */
    public function __construct($items)
    {
        $this->items = $items;
    }
	
    /**
     * Add an item to the collection.
     *
     * @param  TKey  $key
     * @param  TValue  $item
     * @return $this
     */
    public function add($key, $item)
    {
        $this->items[$key] = $item;

        return $this;
    }
}

/** @var Collection<int, int> */
$c = new Collection([1, 2]);

$c->add(2, 3);

Psalm output (using commit 9222b24):

No issues!