# [TWIL] Week of May 12, 2024

Similar to last week, this week was mainly about deploying and upgrading smart contracts. Here are a couple of things I learned:

## Usage of `unchecked`

Looking at many Solidity smart contracts deployed on various mainnets, I noticed the use of the `unchecked` keyword in several instances, especially within for loops. I looked it up on Google and read [this Stack Overflow answer](https://ethereum.stackexchange.com/questions/113221/what-is-the-purpose-of-unchecked-in-solidity). In simple terms, it is a gas-efficient way of handling arithmetic operations by ignoring any possible underflow or overflow errors. In other words, if you know that underflow and overflow will never occur for an arithmetic operation, wrapping it with the `unchecked` keyword will use less gas than the default checked operation. Here's a quick example:

```solidity
contract SmartContract {
    uint[] public intArray;

    function contractMethod() external {
        require(intArray.length < 5, "Length must be less than 5");
        for (uint i; i < intArray.length;) {
            // perform some operation...

            unchecked {
                i++;
            }
        }
    }
}
```

## OpenZeppelin's Proxy Admin Issue

While upgrading and deploying several smart contracts using Hardhat, I encountered an error: `Proxy admin is not the one registered in the network manifest`. I searched online for a solution but found none, except for deleting the entire manifest file in the `.openzeppelin` directory.

Instead, here's how I resolved it:

1. I went to Polygonscan, searched for the contract I was trying to upgrade, and retrieved the proxy admin contract's address by interacting with the website.
    
2. I then checked the `.openzeppelin > polygon.json` file and noticed that the address under `admin` was different from the one I got from Polygonscan.
    
3. I replaced the address in the `polygon.json` file with the one from Polygonscan.
    
4. Finally, I reran the code to upgrade the smart contract, and it worked.
    

So, if you encounter the same issue, find the proxy admin's address from the relevant block explorer and replace the one in the `.openzeppelin > <network>.json` file with it.