Wrapper function to store a balance in eternal storage

set_balance_eternal_storage.sol

function setBalance(address _who, uint256 _value) external {
  setUInt256(
    // computes the Ethereum-SHA-3 (Keccak-256) hash
    keccak256(      
      // performs packed encoding of the given arguments, 
      // as the hash function only accepts one argument
      abi.encodePacked(
        // we use a hardcoded string to create a different 
        // hash for the same dynamic value
        "balance", 
        // a unique dynamic value is needed to clearly 
        // assign the value to an account
        _who
      )
    ), 
    // the value we want to store
    _value                  
  );
}