public function offsetExists($offset): bool
    {
        MDataType::mustBe(array(MDataType::INT));

        return (array_key_exists($offset, $this->list) === true);
    }
public function offsetExists($offset): bool
    {
        MDataType::mustBe(array(MDataType::INT));

        return (array_key_exists($offset, $this->list) === true);
    }
public function offsetExists ( $ offset ) : bool { MDataType :: mustBe ( array ( MDataType :: INT ) ) ; return ( array_key_exists ( $ offset , $ this -> list ) === true ) ; }
Return if a key exists.

@param int $offset
@return bool
Return if a key exists .