Add reset function to Counters library

[simontianx]

🧐 Motivation

In a scenario like moving a point in one direction in a bounded segment, a counter can reach the upper limit and then needs to get reset to start all over again. It would be great if a reset function can be added to the Counters library.

📝 Details

function reset(Counter storage counter) internal {
    counter._value = 0;
}

[Amxx]

Hello issue @xu-tian , and tank for your issue.
This sounds like a reasonable request that is easy to implement!

[simontianx]

You are welcome.

I noticed unchecked is added in the new function, and I also noticed increment and decrement also have unchecked as well. However, by default, the values are checked and will throw when overflow or underflow. Isn't that the right feature to have?

function reset(Counter storage counter) internal {
    unchecked {
        counter._value = 0;
    }
}

[Amxx]

uncheck removed solidity 0.8.0 built-in safe to save some gas. It is in the counter library, because the checks are not needed:

• for increment to overflow, you would need to call it 2**256 times, which is not realistic in this universe
• decrement is already protected for overflow thanks to the require() that will raise an error string.

In reset, assigning 0 doesn't include safemath protection, so unchecked is not needed (and won't do anything good or bad)

[simontianx]

Got it. I did a test and it is indeed using less gas. Thanks for the clarification.