type MaxBits64 = 0|1|2|3|4|5|6|7|8|9|10|11|12|13|14|15|16|17|18|19|20|21|22|23|24|25|26|27|28|29|30|31|32|33|34|35|36|37|38|39|40|41|42|43|44|45|46|47|48|49|50|51|52|53|54|55|56|57|58|59|60|61|62|63;

export function bitmaskMap<
    FlagsT extends (readonly string[] & {
        length: MaxBits,
    }),
    MaxBits extends number = MaxBits64,
>(
    flags: FlagsT,
    startingBitIndex: number = 0,
): {
    [flag in FlagsT[MaxBits]]: number
} {
    const x = flags.reduce((sum, flag, flagIndex) => {
        const bitmask = 1 << (startingBitIndex + flagIndex);
        return Object.assign(sum, {
            [flag]: bitmask
        });
    }, {} as {
        [flag in FlagsT[MaxBits]]: number
    });

    return x;
}