Solidity – Automating Transaction Tax and Distribution to Token Holders

contract-designgassolidity

Is there an efficient way to automatically "tax" every transaction and proportionately send the taxed amount to all non-blacklisted token holders? From my understanding, looping through all addresses upon every transaction will cost an extraordinary amount of gas.

Is it possible to do this by keeping track of a totalTaxedAmount and returning the following when calling balanceOf(address)?

function balanceOf(address addr) public view returns (uint256){
    return balances[addr] + balances[addr]*totalTaxedAmount/totalSupply;
}

Will this actually reflect a token count increase?

Best Answer

Looping over all addresses is definitely not the way. However, you can try keeping track of unique users and the total taxed amount.

A quick sample contract:

pragma solidity 0.8.2;

contract TaxedToken {
    
    
    mapping(address => uint) internal balances;
    mapping(address => bool) internal isTokenHolder;
    uint totalTaxedAmount = 0;
    uint totalUniqueUsers = 0;
    uint tax = 10;
    address public owner;
    
    constructor() {
        owner = msg.sender;
        balances[owner] = 100;
        totalUniqueUsers = 1;
    }
    
    function balanceOf(address account) public view returns (uint) {
        return balances[account] + (totalTaxedAmount / totalUniqueUsers);
    }
    
    function transfer(address _to, uint _value) public {
        require(balanceOf(msg.sender) >= _value, "Insuficient funds");
        balances[msg.sender] =  balances[msg.sender] - _value;
        balances[_to] = balances[_to]  + _value - tax;
        if(!isTokenHolder[_to]) {
            isTokenHolder[_to] =  true;
            totalUniqueUsers++;
        }
        totalTaxedAmount += tax;
    }
}

Do take care of edge cases like:

A new recipient is awarded "tax reward" on the past transactions which reduces others' share.
When the sender transfers all his funds; he should be removed from isTokenHolder mapping

Related Solutions

Token Holders – How to Find All Token Holders in Solidity

All token transfers are performed by calling methods on your contract - so your contract can track balances and accounts in any way it wishes. If you're using the default arrangement of using a Solidity mapping, you will also need to keep a separate list of known account IDs in an array, so you can iterate over them.

[Ethereum] How to send some ether to all token holders

There's some trickiness when sending ether to lots of recipients.

If you use address.send(), the send can fail if the recipient is a contract that consumes some gas, because send() only forwards a fixed amount of gas. So (a) you don't want to throw if send returns false, because it would block everybody, and (b) that recipient will never get the ether, no matter how much gas he includes.

The other way is to use address.call.value, which does forward all gas. But you don't want to use that in this situation because a contract that consumes all the gas will halt everything even if you don't throw upon failure. So if you insist on looping the sends, you have to use address.send() and ignore failures.

To make sure everyone can get their ether, have each recipient call a withdraw() method in your contract. Within that method, do whatever update you need to record the withdrawal, then say "if (!address.call.value(x)()) throw;". If the recipient doesn't include enough gas, everything gets rolled back and he can try again.

If you do this, you no longer have to worry about finding all token holders. This also prevents the problem of having so many people in the loop that you exceed the gas limit of the entire block.

But if you really want to loop and address.send, then you're going to need a data structure like this:

mapping(address => uint) public holders; //people's balances
mapping(uint => address) public indexes;
uint public topindex;

Every time you add a token holder, you increment topindex, put the new index and holder address in indexes, and the address and balance in holders. This is necessary because there's no native way to iterate through a mapping, which is because of the way the mapping is stored in the blockchain.

Anything marked "public" is accessible from other contracts.

Best Answer

Related Solutions

Token Holders – How to Find All Token Holders in Solidity

[Ethereum] How to send some ether to all token holders

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