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<?php |
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namespace Michaelc\Voting\STV; |
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use Michaelc\Voting\STV\{Election, Ballot, Candidate}; |
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class VoteHandler |
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{ |
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/** |
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* Election object |
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* |
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* @var \Michaelc\Voting\STV\Election; |
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*/ |
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protected $election; |
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/** |
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* Array of all ballots in election |
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* |
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* @var \MichaelC\Voting\STV\Ballot[] |
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*/ |
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protected $ballots; |
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/** |
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* Quota of votes needed for a candidate to be elected |
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* |
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* @var int |
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*/ |
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protected $quota; |
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/** |
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* Number of candidates elected so far |
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* |
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* @var int |
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*/ |
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protected $electedCandidates; |
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/** |
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* Constructor |
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* |
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* @param Election $election |
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*/ |
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public function __construct(Election $election) |
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{ |
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$this->election = $election; |
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$this->ballots = $this->election->getBallots(); |
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$this->quota = $this->getQuota(); |
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} |
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/** |
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* Run the election |
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* |
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* @return \MichaelC\Voting\STV\Candidate[] Winning candidates |
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*/ |
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public function run() |
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{ |
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$this->firstStep(); |
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$candidates = $this->election->getActiveCandidates(); |
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while ($electedCandidates < $this->election->getWinners()) |
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{ |
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if (!$this->checkCandidates($candidates)) |
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{ |
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$this->eliminateCandidates($candidates); |
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} |
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} |
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return $this->election->getElectedCandidates(); |
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} |
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/** |
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* Perform the initial vote allocation |
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* |
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* @return |
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*/ |
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public function firstStep() |
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{ |
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foreach ($this->ballots as $i => $ballot) |
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{ |
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$this->allocateVotes($ballot); |
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} |
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return; |
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} |
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/** |
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* Check if any candidates have reached the quota and can be elected |
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* |
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* @param array $candidates Array of active candidates to check |
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* @return bool Whether any candidates were changed to elected |
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*/ |
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protected function checkCandidates(array &$candidates): bool |
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{ |
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foreach ($candidates as $i => $candidate) |
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{ |
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if ($candidate->getVotes() >= $this->quota) |
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{ |
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$this->electCandidate($candidate); |
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$elected = true; |
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} |
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} |
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return $elected ?? false; |
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} |
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/** |
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* Allocate the next votes from a Ballot |
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* |
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* @param Ballot $ballot The ballot to allocate the votes from |
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* @param float $multiplier Number to multiply the weight by (surplus) |
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* @param float $divisor The divisor of the weight (Total number of |
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* candidate votes) |
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* @return Ballot The same ballot passed in modified |
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*/ |
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protected function allocateVotes(Ballot &$ballot, float $multiplier = 1.0, float $divisor = 1.0): Ballot |
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{ |
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$weight = $ballot->setWeight(($ballot->getWeight() * $multiplier) / $divisor); |
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$candidate = $ballot->getNextChoice(); |
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if ($candidate !== null) |
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{ |
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$this->election->getCandidate($candidate->getId())->addVotes($weight); |
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$ballot->setLevelUsed(($step - 1)); |
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} |
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return $ballot; |
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} |
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/** |
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* Transfer the votes from one candidate to other candidates |
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* |
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* @param float $surplus The number of surplus votes to transfer |
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* @param Candidate $candidate The candidate being elected to transfer |
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* the votes from |
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* @return |
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*/ |
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protected function transferSurplusVotes(float $surplus, Candidate $candidate) |
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{ |
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$totalVotes = $candiate->getVotes(); |
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$candidateId = $candidate->getId(); |
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foreach ($this->ballots as $i => $ballot) |
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{ |
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if ($ballot->getLastChoice()->getId() == $candidateId) |
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{ |
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$this->allocateVotes($ballot, $surplus, $totalVotes); |
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} |
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} |
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return; |
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} |
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/** |
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* Transfer the votes from one eliminated candidate to other candidates |
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* |
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* @param Candidate $candidate Candidate being eliminated to transfer |
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* the votes from |
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* @return |
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*/ |
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protected function transferEliminatedVotes(Candidate $candidate) |
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{ |
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$candidateId = $candidate->getId(); |
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foreach ($this->ballots as $i => $ballot) |
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{ |
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if ($ballot->getLastChoice()->getId() == $candidateId) |
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{ |
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$this->allocateVotes($ballot); |
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} |
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} |
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return; |
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} |
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/** |
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* Elect a candidate after they've passed the threshold |
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* |
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* @param \Michaelc\Voting\STV\Candidate $candidate |
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* @return null |
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*/ |
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protected function electCandidate(Candidate $candidate) |
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{ |
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if ($candidate->getVotes() < $this->quota) |
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{ |
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throw new Exception("We shouldn't be electing someone who hasn't met the quota"); |
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} |
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$candidate->setState(Candidate::ELECTED); |
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$this->electedCandidates++; |
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if ($this->electedCandidates < $this->election->getWinnersCount()) |
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{ |
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$surplus = $candidate->getVotes() - $this->quota; |
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$this->transferVotes($surplus, $candidate); |
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} |
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return; |
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} |
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/** |
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* Eliminate the candidate(s) with the lowest number of votes |
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* and reallocated their votes |
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* |
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* @param array $candidates Array of active candidates |
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* @return int Number of candidates eliminated |
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*/ |
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protected function eliminateCandidates(array &$candidates): int |
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{ |
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$minimum = 0; |
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foreach ($candidates as $i => $candidate) |
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{ |
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if ($candidate->getVotes() > $minimum) |
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{ |
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$minimum = $candidate->getVotes(); |
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unset($minimumCandidates); |
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$minimumCandidates[] = $candidate; |
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} |
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elseif ($candidate->getVotes() == $minimum) |
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{ |
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$minimumCandidates[] = $candidate; |
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} |
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} |
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foreach($minimumCandidates as $minimumCandidate) |
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{ |
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$this->transferEliminatedVotes($minimumCandidate); |
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$minimumCandidate->setState(Candidate::DEFEATED); |
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} |
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return count($minimumCandidates); |
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} |
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/** |
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* Get the quota to win |
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* |
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* @return int |
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*/ |
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public function getQuota(): int |
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{ |
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return floor( |
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($this->election->getNumBallots() / |
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($this->election->getWinnersCount() + 1) |
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) |
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+ 1); |
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} |
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} |
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Let’s assume that you have a directory layout like this:
. |-- OtherDir | |-- Bar.php | `-- Foo.php `-- SomeDir `-- Foo.phpand let’s assume the following content of
Bar.php:If both files
OtherDir/Foo.phpandSomeDir/Foo.phpare loaded in the same runtime, you will see a PHP error such as the following:PHP Fatal error: Cannot use SomeDir\Foo as Foo because the name is already in use in OtherDir/Foo.phpHowever, as
OtherDir/Foo.phpdoes not necessarily have to be loaded and the error is only triggered if it is loaded beforeOtherDir/Bar.php, this problem might go unnoticed for a while. In order to prevent this error from surfacing, you must import the namespace with a different alias: