[Pure]
        public static ushort? ToUInt16(
            [CanBeNull] this string str,
            NumberStyles numberStyle = NumberStyles.Integer,
            [CanBeNull] IFormatProvider provider = null)
        {
            ushort result;
            return ushort.TryParse(str, numberStyle, provider, out result) ? (ushort?)result : null;
        }

        [Pure]
        public static ushort? ToUInt16Invariant(
            [CanBeNull] this string str,
            NumberStyles numberStyle = NumberStyles.Integer)
        {
            ushort result;
            return ushort.TryParse(str, numberStyle,  CultureInfo.InvariantCulture, out result) ? (ushort?)result : null;
        }

        [Pure]
        public static int? ToInt32(
            [CanBeNull] this string str,
            NumberStyles numberStyle = NumberStyles.Integer,
            [CanBeNull] IFormatProvider provider = null)
        {
            int result;
            return int.TryParse(str, numberStyle, provider, out result) ? (int?)result : null;
        }

        [Pure]
        public static int? ToInt32Invariant(
            [CanBeNull] this string str,
            NumberStyles numberStyle = NumberStyles.Integer)
        {
            int result;
            return int.TryParse(str, numberStyle,  CultureInfo.InvariantCulture, out result) ? (int?)result : null;
        }