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38. Building a staking contract

Accounting, reward rate and withdrawals.

1 min read3 questionsup to 50 XPtopic 38/50

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A simple staking contract tracks each user's balance and the time of their last update, then accrues rewards as `amount * rate * elapsed`. Update the accrual *before* changing a balance, or a deposit would retroactively earn.

solidity
function _accrue(address u) internal {
    Position storage p = positions[u];
    rewards[u] += p.amount * rate * (block.timestamp - p.since) / 1e18;
    p.since = uint64(block.timestamp);
}

Keep the reward pool funded separately from principal so a withdrawal can never spend another user's stake.

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Check your understanding

  1. 1. When must rewards be accrued?

  2. 2. Why separate reward funds from principal?

  3. 3. What variable does accrual depend on?

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