mirror of
https://github.com/ethereum/solidity
synced 2023-10-03 13:03:40 +00:00
Update common-patterns.rst
This commit is contained in:
Matt Wisniewski
chriseth
parent
00933b99cc
commit
2b4b86aa7f
@ -28,7 +28,7 @@ become the new richest.
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::
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pragma solidity ^0.4.0;
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pragma solidity ^0.4.11;
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contract WithdrawalContract {
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address public richest;
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@ -70,7 +70,7 @@ This is as opposed to the more intuitive sending pattern:
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::
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pragma solidity ^0.4.0;
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pragma solidity ^0.4.11;
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contract SendContract {
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address public richest;
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@ -86,9 +86,7 @@ This is as opposed to the more intuitive sending pattern:
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// Check if call succeeds to prevent an attacker
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// from trapping the previous person's funds in
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// this contract through a callstack attack
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if (!richest.send(msg.value)) {
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throw;
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}
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richest.transfer(msg.value);
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richest = msg.sender;
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mostSent = msg.value;
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return true;
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@ -135,7 +133,7 @@ restrictions highly readable.
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::
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pragma solidity ^0.4.0;
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pragma solidity ^0.4.11;
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contract AccessRestriction {
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// These will be assigned at the construction
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@ -152,8 +150,7 @@ restrictions highly readable.
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// a certain address.
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modifier onlyBy(address _account)
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{
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if (msg.sender != _account)
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throw;
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require(msg.sender == _account);
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// Do not forget the "_;"! It will
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// be replaced by the actual function
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// body when the modifier is used.
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@ -169,7 +166,7 @@ restrictions highly readable.
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}
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modifier onlyAfter(uint _time) {
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if (now < _time) throw;
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require(now >= _time);
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_;
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}
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@ -190,8 +187,7 @@ restrictions highly readable.
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// This was dangerous before Solidity version 0.4.0,
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// where it was possible to skip the part after `_;`.
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modifier costs(uint _amount) {
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if (msg.value < _amount)
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throw;
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require(msg.value >= _amount);
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_;
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if (msg.value > _amount)
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msg.sender.send(msg.value - _amount);
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@ -276,7 +272,7 @@ function finishes.
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::
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pragma solidity ^0.4.0;
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pragma solidity ^0.4.11;
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contract StateMachine {
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enum Stages {
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@ -293,7 +289,7 @@ function finishes.
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uint public creationTime = now;
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modifier atStage(Stages _stage) {
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if (stage != _stage) throw;
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require(stage == _stage);
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_;
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}
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@ -327,7 +327,7 @@ inheritable properties of contracts and may be overridden by derived contracts.
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::
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pragma solidity ^0.4.0;
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pragma solidity ^0.4.11;
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contract owned {
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function owned() { owner = msg.sender; }
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@ -341,8 +341,7 @@ inheritable properties of contracts and may be overridden by derived contracts.
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// function is executed and otherwise, an exception is
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// thrown.
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modifier onlyOwner {
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if (msg.sender != owner)
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throw;
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require(msg.sender == owner);
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_;
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}
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}
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@ -390,7 +389,7 @@ inheritable properties of contracts and may be overridden by derived contracts.
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contract Mutex {
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bool locked;
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modifier noReentrancy() {
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if (locked) throw;
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require(!locked);
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locked = true;
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_;
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locked = false;
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@ -401,7 +400,7 @@ inheritable properties of contracts and may be overridden by derived contracts.
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/// The `return 7` statement assigns 7 to the return value but still
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/// executes the statement `locked = false` in the modifier.
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function f() noReentrancy returns (uint) {
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if (!msg.sender.call()) throw;
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require(msg.sender.call());
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return 7;
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}
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}
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@ -989,7 +988,7 @@ more advanced example to implement a set).
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::
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pragma solidity ^0.4.0;
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pragma solidity ^0.4.11;
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library Set {
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// We define a new struct datatype that will be used to
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@ -1035,8 +1034,7 @@ more advanced example to implement a set).
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// The library functions can be called without a
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// specific instance of the library, since the
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// "instance" will be the current contract.
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if (!Set.insert(knownValues, value))
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throw;
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assert(Set.insert(knownValues, value));
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}
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// In this contract, we can also directly access knownValues.flags, if we want.
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}
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@ -1166,7 +1164,7 @@ available without having to add further code.
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Let us rewrite the set example from the
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:ref:`libraries` in this way::
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pragma solidity ^0.4.0;
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pragma solidity ^0.4.11;
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// This is the same code as before, just without comments
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library Set {
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@ -1207,8 +1205,7 @@ Let us rewrite the set example from the
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// corresponding member functions.
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// The following function call is identical to
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// Set.insert(knownValues, value)
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if (!knownValues.insert(value))
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throw;
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require(knownValues.insert(value));
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}
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}
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@ -665,8 +665,7 @@ What does the following strange check do in the Custom Token contract?
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::
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if (balanceOf[_to] + _value < balanceOf[_to])
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throw;
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require(balanceOf[_to] + _value >= balanceOf[_to]);
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Integers in Solidity (and most other machine-related programming languages) are restricted to a certain range.
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For ``uint256``, this is ``0`` up to ``2**256 - 1``. If the result of some operation on those numbers
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@ -79,7 +79,7 @@ outlined further below:
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::
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pragma solidity ^0.4.0;
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pragma solidity ^0.4.11;
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contract Fund {
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/// Mapping of ether shares of the contract.
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@ -88,8 +88,7 @@ outlined further below:
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function withdraw() {
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var share = shares[msg.sender];
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shares[msg.sender] = 0;
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if (!msg.sender.send(share))
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throw;
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require(msg.sender.send(share));
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}
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}
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@ -162,7 +161,7 @@ Never use tx.origin for authorization. Let's say you have a wallet contract like
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::
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pragma solidity ^0.4.0;
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pragma solidity ^0.4.11;
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// THIS CONTRACT CONTAINS A BUG - DO NOT USE
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contract TxUserWallet {
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@ -173,8 +172,8 @@ Never use tx.origin for authorization. Let's say you have a wallet contract like
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}
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function transfer(address dest, uint amount) {
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if (tx.origin != owner) { throw; }
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if (!dest.call.value(amount)()) throw;
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require(tx.origin == owner);
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require(dest.call.value(amount)());
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}
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}
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@ -36,7 +36,7 @@ of votes.
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::
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pragma solidity ^0.4.0;
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pragma solidity ^0.4.11;
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/// @title Voting with delegation.
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contract Ballot {
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@ -87,14 +87,12 @@ of votes.
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// Give `voter` the right to vote on this ballot.
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// May only be called by `chairperson`.
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function giveRightToVote(address voter) {
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if (msg.sender != chairperson || voters[voter].voted) {
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// `throw` terminates and reverts all changes to
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// the state and to Ether balances. It is often
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// a good idea to use this if functions are
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// called incorrectly. But watch out, this
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// will also consume all provided gas.
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throw;
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}
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require(msg.sender == chairperson || !voters[voter].voted);
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voters[voter].weight = 1;
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}
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@ -102,12 +100,10 @@ of votes.
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function delegate(address to) {
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// assigns reference
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Voter sender = voters[msg.sender];
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if (sender.voted)
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throw;
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require(!sender.voted);
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// Self-delegation is not allowed.
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if (to == msg.sender)
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throw;
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require(to != msg.sender);
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// Forward the delegation as long as
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// `to` also delegated.
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@ -121,8 +117,7 @@ of votes.
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to = voters[to].delegate;
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// We found a loop in the delegation, not allowed.
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if (to == msg.sender)
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throw;
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require(to != msg.sender);
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}
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// Since `sender` is a reference, this
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@ -145,8 +140,7 @@ of votes.
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/// to proposal `proposals[proposal].name`.
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function vote(uint proposal) {
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Voter sender = voters[msg.sender];
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if (sender.voted)
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throw;
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require(!sender.voted);
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sender.voted = true;
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sender.vote = proposal;
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@ -218,7 +212,7 @@ activate themselves.
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::
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pragma solidity ^0.4.0;
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pragma solidity ^0.4.11;
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contract SimpleAuction {
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// Parameters of the auction. Times are either
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@ -269,16 +263,16 @@ activate themselves.
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// the transaction. The keyword payable
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// is required for the function to
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// be able to receive Ether.
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if (now > auctionStart + biddingTime) {
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// Revert the call if the bidding
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// period is over.
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throw;
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}
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if (msg.value <= highestBid) {
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require(now < auctionStart + biddingTime);
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// If the bid is not higher, send the
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// money back.
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throw;
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}
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require(msg.value <= highestBid);
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if (highestBidder != 0) {
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// Sending back the money by simply using
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// highestBidder.send(highestBid) is a security risk
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@ -327,18 +321,15 @@ activate themselves.
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// external contracts.
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// 1. Conditions
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if (now <= auctionStart + biddingTime)
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throw; // auction did not yet end
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if (ended)
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throw; // this function has already been called
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require(now >= auctionStart + biddingTime); // auction did not yet end
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require(!ended); // this function has already been called
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// 2. Effects
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ended = true;
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AuctionEnded(highestBidder, highestBid);
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// 3. Interaction
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if (!beneficiary.send(highestBid))
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throw;
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require(beneficiary.transfer(highestBid));
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}
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}
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@ -381,7 +372,7 @@ high or low invalid bids.
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::
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pragma solidity ^0.4.0;
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pragma solidity ^0.4.11;
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contract BlindAuction {
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struct Bid {
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@ -409,8 +400,8 @@ high or low invalid bids.
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/// functions. `onlyBefore` is applied to `bid` below:
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/// The new function body is the modifier's body where
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/// `_` is replaced by the old function body.
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modifier onlyBefore(uint _time) { if (now >= _time) throw; _; }
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modifier onlyAfter(uint _time) { if (now <= _time) throw; _; }
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modifier onlyBefore(uint _time) { require(!now >= _time); _; }
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modifier onlyAfter(uint _time) { require(!now <= _time); _; }
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function BlindAuction(
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uint _biddingTime,
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@ -454,13 +445,11 @@ high or low invalid bids.
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onlyBefore(revealEnd)
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{
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uint length = bids[msg.sender].length;
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if (
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_values.length != length ||
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_fake.length != length ||
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_secret.length != length
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) {
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throw;
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}
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require(
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_values.length == length ||
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_fake.length == length ||
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_secret.length == length
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);
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uint refund;
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for (uint i = 0; i < length; i++) {
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@ -481,8 +470,7 @@ high or low invalid bids.
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// the same deposit.
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bid.blindedBid = 0;
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}
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if (!msg.sender.send(refund))
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throw;
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msg.sender.transfer(refund);
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}
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// This is an "internal" function which means that it
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@ -527,14 +515,12 @@ high or low invalid bids.
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function auctionEnd()
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onlyAfter(revealEnd)
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{
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if (ended)
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throw;
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require(!ended);
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AuctionEnded(highestBidder, highestBid);
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ended = true;
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// We send all the money we have, because some
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// of the refunds might have failed.
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if (!beneficiary.send(this.balance))
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throw;
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beneficiary.transfer(this.balance);
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}
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}
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@ -546,7 +532,7 @@ Safe Remote Purchase
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::
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pragma solidity ^0.4.0;
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pragma solidity ^0.4.11;
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contract Purchase {
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uint public value;
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@ -558,26 +544,26 @@ Safe Remote Purchase
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function Purchase() payable {
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seller = msg.sender;
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value = msg.value / 2;
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if (2 * value != msg.value) throw;
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require(!2 * value != msg.value);
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}
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modifier require(bool _condition) {
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if (!_condition) throw;
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require(_condition);
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_;
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}
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modifier onlyBuyer() {
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if (msg.sender != buyer) throw;
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require(msg.sender == buyer);
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_;
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}
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modifier onlySeller() {
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if (msg.sender != seller) throw;
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require(msg.sender == seller);
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_;
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}
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modifier inState(State _state) {
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if (state != _state) throw;
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require(state == _state);
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_;
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}
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@ -594,8 +580,7 @@ Safe Remote Purchase
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{
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aborted();
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state = State.Inactive;
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if (!seller.send(this.balance))
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throw;
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seller.transfer(this.balance);
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}
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/// Confirm the purchase as buyer.
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@ -625,8 +610,7 @@ Safe Remote Purchase
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state = State.Inactive;
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// This actually allows both the buyer and the seller to
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// block the refund.
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if (!buyer.send(value) || !seller.send(this.balance))
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throw;
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require(buyer.transfer(value) || seller.transfer(this.balance));
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}
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}
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@ -62,13 +62,13 @@ Function modifiers can be used to amend the semantics of functions in a declarat
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::
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pragma solidity ^0.4.0;
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pragma solidity ^0.4.11;
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contract Purchase {
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address public seller;
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modifier onlySeller() { // Modifier
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if (msg.sender != seller) throw;
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require(msg.sender == seller);
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_;
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}
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@ -420,7 +420,7 @@ Example that shows how to use internal function types::
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Another example that uses external function types::
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pragma solidity ^0.4.5;
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pragma solidity ^0.4.11;
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contract Oracle {
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struct Request {
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@ -445,7 +445,7 @@ Another example that uses external function types::
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oracle.query("USD", this.oracleResponse);
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}
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function oracleResponse(bytes response) {
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if (msg.sender != address(oracle)) throw;
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require(msg.sender == address(oracle));
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// Use the data
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}
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}
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@ -722,7 +722,7 @@ shown in the following example:
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::
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pragma solidity ^0.4.0;
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pragma solidity ^0.4.11;
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contract CrowdFunding {
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// Defines a new type with two fields.
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@ -763,8 +763,7 @@ shown in the following example:
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return false;
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uint amount = c.amount;
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c.amount = 0;
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if (!c.beneficiary.send(amount))
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throw;
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c.beneficiary.transfer(amount);
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return true;
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}
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}
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