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August 2, 2017 17:32
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pragma solidity ^0.4.11; | |
/// @title Voting with delegation. | |
contract Ballot { | |
struct Voter { | |
uint weight; // weight is accumulated by delegation | |
bool voted; // if true, that person already voted | |
address delegate; // person delegated to | |
uint vote; // index of the voted proposal | |
} | |
// This is a type for a single proposal. | |
struct Proposal { | |
bytes32 name; // short name (up to 32 bytes) | |
uint voteCount; // number of accumulated votes | |
} | |
address public chairperson; | |
// This declares a state variable that | |
// stores a `Voter` struct for each possible address. | |
mapping(address => Voter) public voters; | |
// A dynamically-sized array of `Proposal` structs. | |
Proposal[] public proposals; | |
/// Create a new ballot to choose one of `proposalNames`. | |
function Ballot(bytes32[] proposalNames) { | |
chairperson = msg.sender; | |
voters[chairperson].weight = 1; | |
// For each of the provided proposal names, | |
// create a new proposal object and add it | |
// to the end of the array. | |
for (uint i = 0; i < proposalNames.length; i++) { | |
// `Proposal({...})` creates a temporary | |
// Proposal object and `proposals.push(...)` | |
// appends it to the end of `proposals`. | |
proposals.push(Proposal({ | |
name: proposalNames[i], | |
voteCount: 0 | |
})); | |
} | |
} | |
// Give `voter` the right to vote on this ballot. | |
// May only be called by `chairperson`. | |
function giveRightToVote(address voter) { | |
// If the argument of `require` evaluates to `false`, | |
// it terminates and reverts all changes to | |
// the state and to Ether balances. It is often | |
// a good idea to use this if functions are | |
// called incorrectly. But watch out, this | |
// will currently also consume all provided gas | |
// (this is planned to change in the future). | |
require((msg.sender == chairperson) && !voters[voter].voted && (voters[voter].weight == 0)); | |
voters[voter].weight = 1; | |
} | |
/// Delegate your vote to the voter `to`. | |
function delegate(address to) { | |
// assigns reference | |
Voter storage sender = voters[msg.sender]; | |
require(!sender.voted); | |
// Self-delegation is not allowed. | |
require(to != msg.sender); | |
// Forward the delegation as long as | |
// `to` also delegated. | |
// In general, such loops are very dangerous, | |
// because if they run too long, they might | |
// need more gas than is available in a block. | |
// In this case, the delegation will not be executed, | |
// but in other situations, such loops might | |
// cause a contract to get "stuck" completely. | |
while (voters[to].delegate != address(0)) { | |
to = voters[to].delegate; | |
// We found a loop in the delegation, not allowed. | |
require(to != msg.sender); | |
} | |
// Since `sender` is a reference, this | |
// modifies `voters[msg.sender].voted` | |
sender.voted = true; | |
sender.delegate = to; | |
Voter delegate = voters[to]; | |
if (delegate.voted) { | |
// If the delegate already voted, | |
// directly add to the number of votes | |
proposals[delegate.vote].voteCount += sender.weight; | |
} else { | |
// If the delegate did not vote yet, | |
// add to her weight. | |
delegate.weight += sender.weight; | |
} | |
} | |
/// Give your vote (including votes delegated to you) | |
/// to proposal `proposals[proposal].name`. | |
function vote(uint proposal) { | |
Voter storage sender = voters[msg.sender]; | |
require(!sender.voted); | |
sender.voted = true; | |
sender.vote = proposal; | |
// If `proposal` is out of the range of the array, | |
// this will throw automatically and revert all | |
// changes. | |
proposals[proposal].voteCount += sender.weight; | |
} | |
/// @dev Computes the winning proposal taking all | |
/// previous votes into account. | |
function winningProposal() constant returns (uint winningProposal){ | |
uint winningVoteCount = 0; | |
for (uint p = 0; p < proposals.length; p++) { | |
if (proposals[p].voteCount > winningVoteCount) { | |
winningVoteCount = proposals[p].voteCount; | |
winningProposal = p; | |
} | |
} | |
} | |
// Calls winningProposal() function to get the index | |
// of the winner contained in the proposals array and then | |
// returns the name of the winner | |
function winnerName() constant | |
returns (bytes32 winnerName) | |
{ | |
winnerName = proposals[winningProposal()].name; | |
} | |
} |
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