Blocklist

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Blocklist
Block addresses from being selected for award distribution
Introduction
The blocklist feature (introduced in 3.4.0) allows the MultipleWinners prize strategy smart contract to prevent addresses from being eligible for winning a prize. 
⚠️ WARNING: The blocklist feature SHOULD NOT be used to prevent normal users from being eligible to win a prize. The intended use case is to prevent smart contracts, which are unable to withdraw prizes.
Why
The blocklist feature was built specifically to overcome the problem of adding tickets to decentralized exchange, so users can easily exchange assets for a ticket in their desired PrizePool without awarding the liquidity pool address with a prize.
Depositing directly into existing PrizePools like USDC and DAI on average costs between 450,000 to 550,000 gas. During times of gas costs (e.x. between 90 - 200+) these can be cost prohibitive for users depositing smaller amounts.
Side Effects of Blocked Addresses When Selecting Winners
In certain circumstances it's possible to select few winners, then the amount designated by the internal __numberOfWinners variable due to the number of attempts (limited by blocklistRetryCount) available in the _distribute function.
For example, if a Uniswap liquidity pool holds 50% of the available tickets, but is blocked from winning, and the number of winners is set to 3 and the try attempt is limited to 5, it's possible the liquidity pool address would be selected 5 times, before 3 winners are randomly drawn.
Resulting in only 2 of 3 winners being selected before the blocklistRetryCountceiling was reached. Depending on the state of carryOverBlocklist the 2 of 3 selected winners would either...
A) split the total awarded prize evenly in this draw period.
B) split the total awarded prize based off __numberOfWinners
If Scenario B occurs the remaining awarded interest would roll over to next draw period. In the next draw period the increased prize amount (due to the carried over prize) would be given to the selected prize.
In every scenario the selected winner(s) will always receive the expected prize amount.
How It Works
The MultipleWinners smart contract now includes the ability to block individual address from being selected as a winner for prize distribution.  
Public Functions
setBlocklisted
setCarryBlocklist
setBlocklistRetryCount
Blocking Address from Winning
A simple mapping called isBlocklisted correlates a user address isBlocked boolean status.
mapping(address => bool) public isBlocklisted;
During the contract initialization all address default isBlocked false. After the contract has been initialized the contract owner can toggle a user's isBlocklisted status by calling setBlocklisted with the _user address and _isBlocked set true.
function setBlocklisted(address _user, bool _isBlocked) external onlyOwner requireAwardNotInProgress returns (bool) {
    isBlocklisted[_user] = _isBlocked;
​
    emit BlocklistSet(_user, _isBlocked);
​
    return true;
  }
To reverse the isBlocked status a contract owner calls the same function. Passing the same _user address with the _isBlockedset false. 
When winners are being selected during
Blocklist Retry Attempt Count
When attempting to select a winner during the draw process it's still possible to select a blocked address. However, instead of adding the blocked address to the array of winners, the contract will attempt to select a new winner with a false isBlocked status.
By default the blocklistRetryCount will be set to 0.
To update the retry count a contract owner can call setBlocklistRetryCount with the number of retries.  
function setBlocklistRetryCount(uint256 _count) external onlyOwner requireAwardNotInProgress returns (bool) {
  blocklistRetryCount = _count;
​
  emit BlocklistRetryCountSet(_count);
​
  return true;
}
As you already know, each Ethereum transaction consumes gas. The more complex a transaction the higher the gas costs. To avoid running out of gas in a if a blocked address is selected multiple times, a retry limit is set and the transaction will continue with awarding the selected winners.
In short, the prize strategy will do its best to select winners without running out of gas.
It's important to mention, even though a a retry attempt count must be set, it's very unlikely the retry attempt limit be reached, unless a blocked address holds an unusually high amount of tickets. 
Prize Award Carry Over
In the very unlikely circumstance the retry count is reached due to a high number of tickets held by a blocked address and the maximum number of winners has not been selected, the prize strategy must decide how to handle the remaining awarded interest: evenly split the interest between selected winners or carry over the interest for the next draw.
By default the award interest is carried over to the next round if the maximum of winners IS NOT selected.
To evenly split the interest between winners the contract owner calls setCarryBlocklist with true.
function setCarryBlocklist(bool _carry) external onlyOwner requireAwardNotInProgress returns (bool) {
  carryOverBlocklist = _carry;
​
  emit BlocklistCarrySet(_carry);
​
  return true;
}
External ERC20 Carry Over
If a PrizeStrategy also awards external ERC20 tokens during award distribution the same carry over rules to the external tokens. In other words, if the main prize is split evenly between the selected winners or carried over to the next draw period, the same logic will be applied to the tokens.
Smart Contract Functions  
Last modified 1yr ago
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Outline
Introduction
Why
Side Effects of Blocked Addresses When Selecting Winners
How It Works
Blocking Address from Winning
Blocklist Retry Attempt Count
Prize Award Carry Over
Smart Contract Functions