/**
* Get key of an array or \ArrayAccess, if both are set.
*
* @param int|string $key the key
* @return Chain the value of the key wrapped into a Chain, or empty Chain
*/
public function getKey($key) : Chain
{
return $this->continue(conditionally(conjunction(is_array_access, function ($value) use($key) {
return isset($value[$key]);
}), array_value_getter($key)));
}
/**
* Find random element of the stream (optionally matched with predicate).
*
* This is a closing operation (it calls <code>$this->close()</code> internally).
*
* @param callable $predicate the predicate (optional)
* @return Optional an optional result
* @see \monad\Stream::close()
*/
public function findRandom(callable $predicate = null) : Optional
{
return $this->bindMonad(sequence(null === $predicate ? conditionally(negation(is_empty), array_value_getter(array_rand($this->val()))) : sequence(traversable_randomize, curry(function ($predicate, array $array) {
return $this->find($predicate, $array);
}, 2)($predicate)), optional));
}