Add Utils Struct EnumerableMap Bytes32ToUintMap

[arturictus]

Adding Bytes32ToUintMap in struct helpers.

PR Checklist

• Tests
• Documentation
• Changelog entry

[Amxx]

Hello @arturictus

Can you tell us more about your usecase for a bytes32 → uint256 map?

[arturictus]

hello @Amxx,
Of course.
I'm building a booking contract which allows to book one night per year.
The approach I'm taking is:

• the frontend will supply (uint16 year, uint16 dayOfTheYear [1-366])
• The bookings and cancellations can not be made to passed dates.
• Each wallet can only book once per year-dayOfTheYear

I use the map as

• key: bytes32(abi.encode(year, dayOftheYear))
• value: timestamp (calculated timestamp to compare to block.timestamp)

This allows me:

• validate uniqueness of the reservation
• Validate time constraints with the timestamp
• create, update and cancel reservations with O(1) complexity
• Be able to iterate over reservations for calculations (done in the client)

I can imagine other use cases:

• key: productID, value: price
• key: saleID, value: time until applicable
• etc, etc

Happy to hear your thoughts

[Amxx]

Thanks for the details. In your case, I would argue that the key could be a uint corresponding to the day's "timestamp". I would consider that safer than bytes32(abi.encode(year, dayOftheYear)) (you are sure you're not doing a hash here ?)

We also have #3338. We'll discuss new mapping types soon

[arturictus]

Hi @Amxx,
Thanks for your response.
Answering your comments:

I would argue that the key could be a uint corresponding to the day's "timestamp"

The problem with that is that a day has 86400 seconds which I can not use timestamp for unique key. (there are some workarounds, but I'm not happy with them)

you are sure you're not doing a hash here ?

Still considering to hash it unless I need to get the original key.
The inputs are validated so they are quite limited in range and always fit in bytes32 range.

[Amxx]

Could you please add a changelog entry?

[arturictus]

Could you please add a changelog entry?

Yes!, done :)