<?php declare(strict_types = 1);

use function PHPStan\dumpType;
use function PHPStan\Testing\assertType;

class Arr
{
	/**
	 * @template TKey of string
	 * @param array<TKey, mixed> $arr
	 * @return ($key is TKey ? true : false)
	 */
	public static function keyExists(array $arr, string $key): bool
	{
		return array_key_exists($key, $arr);
	}
}

dumpType(Arr::keyExists(['a' => 1], 'a')); // true ✓
dumpType(Arr::keyExists(['a' => 1], 'b')); // true ✘ (should be false)
dumpType(Arr::keyExists(['a' => 1, 'b' => 2], 'a')); // true ✓
dumpType(Arr::keyExists(['a' => 1, 'b' => 2], 'b')); // true ✘ (should be false)