It seems like the usual way of handling a failed send in the Solidity docs is to use throw. I was confused when in the withdraw function of the blind auction example they don't use throw and instead manually set the state back to before the call was made. I was wondering why they decided not to use throw here?

        if (!msg.sender.send(amount)){
            // No need to call throw here, just reset the amount owing
            pendingReturns[msg.sender] = amount;
            return false;
  • throw is generally considered "cleaner" in that the state is guaranteed to be rolled back as if the transaction never happened, so most developers choose to use that method. The issue is that this consumes all of the transaction's gas, and it is hard for other contracts to handle the exception gracefully. So in cases where only very simple state changes are made, it can be better to just roll back the changes and exit gracefully. Mar 27, 2017 at 19:58

1 Answer 1


When you use throw during the execution of a function, all changes in the state are reversed and all gas sent by the sender is consumed.

In that function, as it is not modifying other variables of the state, it is enough to reset that variable to its initial value.

They are probably doing it this way instead of using throw to avoid wasting the sender's gas.

  • Doesn't this leave the contract susceptible to ddos? Mar 28, 2017 at 6:03
  • What do you mean by ddos in this case? the sender still needs to spend some gas at market price in order to execute the function.
    – AdrianClv
    Mar 28, 2017 at 8:24
  • I thought the fact that throw uses all gas is supposed to provide additional protection Mar 28, 2017 at 19:56

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