diff options
Diffstat (limited to 'docs/solidity-by-example.rst')
| -rw-r--r-- | docs/solidity-by-example.rst | 114 |
1 files changed, 50 insertions, 64 deletions
diff --git a/docs/solidity-by-example.rst b/docs/solidity-by-example.rst index 3d6221e4..4ed474df 100644 --- a/docs/solidity-by-example.rst +++ b/docs/solidity-by-example.rst @@ -36,7 +36,7 @@ of votes. :: - pragma solidity ^0.4.0; + pragma solidity ^0.4.11; /// @title Voting with delegation. contract Ballot { @@ -87,14 +87,14 @@ of votes. // Give `voter` the right to vote on this ballot. // May only be called by `chairperson`. function giveRightToVote(address voter) { - if (msg.sender != chairperson || voters[voter].voted) { - // `throw` 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 also consume all provided gas. - throw; - } + // 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 = 1; } @@ -102,12 +102,10 @@ of votes. function delegate(address to) { // assigns reference Voter sender = voters[msg.sender]; - if (sender.voted) - throw; + require(!sender.voted); // Self-delegation is not allowed. - if (to == msg.sender) - throw; + require(to != msg.sender); // Forward the delegation as long as // `to` also delegated. @@ -121,8 +119,7 @@ of votes. to = voters[to].delegate; // We found a loop in the delegation, not allowed. - if (to == msg.sender) - throw; + require(to != msg.sender); } // Since `sender` is a reference, this @@ -145,8 +142,7 @@ of votes. /// to proposal `proposals[proposal].name`. function vote(uint proposal) { Voter sender = voters[msg.sender]; - if (sender.voted) - throw; + require(!sender.voted); sender.voted = true; sender.vote = proposal; @@ -218,7 +214,7 @@ activate themselves. :: - pragma solidity ^0.4.0; + pragma solidity ^0.4.11; contract SimpleAuction { // Parameters of the auction. Times are either @@ -269,16 +265,15 @@ activate themselves. // the transaction. The keyword payable // is required for the function to // be able to receive Ether. - if (now > auctionStart + biddingTime) { - // Revert the call if the bidding - // period is over. - throw; - } - if (msg.value <= highestBid) { - // If the bid is not higher, send the - // money back. - throw; - } + + // Revert the call if the bidding + // period is over. + require(now <= (auctionStart + biddingTime)); + + // If the bid is not higher, send the + // money back. + require(msg.value > highestBid); + if (highestBidder != 0) { // Sending back the money by simply using // highestBidder.send(highestBid) is a security risk @@ -327,18 +322,15 @@ activate themselves. // external contracts. // 1. Conditions - if (now <= auctionStart + biddingTime) - throw; // auction did not yet end - if (ended) - throw; // this function has already been called + require(now >= (auctionStart + biddingTime)); // auction did not yet end + require(!ended); // this function has already been called // 2. Effects ended = true; AuctionEnded(highestBidder, highestBid); // 3. Interaction - if (!beneficiary.send(highestBid)) - throw; + beneficiary.transfer(highestBid); } } @@ -381,7 +373,7 @@ high or low invalid bids. :: - pragma solidity ^0.4.0; + pragma solidity ^0.4.11; contract BlindAuction { struct Bid { @@ -409,8 +401,8 @@ high or low invalid bids. /// functions. `onlyBefore` is applied to `bid` below: /// The new function body is the modifier's body where /// `_` is replaced by the old function body. - modifier onlyBefore(uint _time) { if (now >= _time) throw; _; } - modifier onlyAfter(uint _time) { if (now <= _time) throw; _; } + modifier onlyBefore(uint _time) { require(now < _time); _; } + modifier onlyAfter(uint _time) { require(now > _time); _; } function BlindAuction( uint _biddingTime, @@ -454,13 +446,9 @@ high or low invalid bids. onlyBefore(revealEnd) { uint length = bids[msg.sender].length; - if ( - _values.length != length || - _fake.length != length || - _secret.length != length - ) { - throw; - } + require(_values.length == length); + require(_fake.length == length); + require(_secret.length == length); uint refund; for (uint i = 0; i < length; i++) { @@ -481,8 +469,7 @@ high or low invalid bids. // the same deposit. bid.blindedBid = 0; } - if (!msg.sender.send(refund)) - throw; + msg.sender.transfer(refund); } // This is an "internal" function which means that it @@ -527,14 +514,12 @@ high or low invalid bids. function auctionEnd() onlyAfter(revealEnd) { - if (ended) - throw; + require(!ended); AuctionEnded(highestBidder, highestBid); ended = true; // We send all the money we have, because some // of the refunds might have failed. - if (!beneficiary.send(this.balance)) - throw; + beneficiary.transfer(this.balance); } } @@ -546,7 +531,7 @@ Safe Remote Purchase :: - pragma solidity ^0.4.0; + pragma solidity ^0.4.11; contract Purchase { uint public value; @@ -558,26 +543,26 @@ Safe Remote Purchase function Purchase() payable { seller = msg.sender; value = msg.value / 2; - if (2 * value != msg.value) throw; + require((2 * value) == msg.value); } - modifier require(bool _condition) { - if (!_condition) throw; + modifier condition(bool _condition) { + require(_condition); _; } modifier onlyBuyer() { - if (msg.sender != buyer) throw; + require(msg.sender == buyer); _; } modifier onlySeller() { - if (msg.sender != seller) throw; + require(msg.sender == seller); _; } modifier inState(State _state) { - if (state != _state) throw; + require(state == _state); _; } @@ -594,8 +579,7 @@ Safe Remote Purchase { aborted(); state = State.Inactive; - if (!seller.send(this.balance)) - throw; + seller.transfer(this.balance); } /// Confirm the purchase as buyer. @@ -604,7 +588,7 @@ Safe Remote Purchase /// is called. function confirmPurchase() inState(State.Created) - require(msg.value == 2 * value) + condition(msg.value == (2 * value)) payable { purchaseConfirmed(); @@ -623,10 +607,12 @@ Safe Remote Purchase // otherwise, the contracts called using `send` below // can call in again here. state = State.Inactive; - // This actually allows both the buyer and the seller to - // block the refund. - if (!buyer.send(value) || !seller.send(this.balance)) - throw; + + // NOTE: This actually allows both the buyer and the seller to + // block the refund - the withdraw pattern should be used. + + buyer.transfer(value); + seller.transfer(this.balance)); } } |