以太坊学习笔记day5
storage和memory
https://solidity.readthedocs.io/en/v0.4.21/types.html#data-location
Every complex type, i.e. arrays and structs, has an additional annotation, the “data location”, about whether it is stored in memory or in storage. Depending on the context, there is always a default, but it can be overridden by appending either storage or memory to the type. The default for function parameters (including return parameters) is memory, the default for local variables is storage and the location is forced to storage for state variables (obviously).
每个复杂的类型, 例如: 数组和结构体, 都额外有一个声明,叫做"数据存储位置"来指定存储在内存还是硬盘.到底存储在哪, 默认情况下取决于上下文, 但是可以用`storage`和 `memory`来显示声明.函数的参数和函数的返回值默认都是`memory`, 而局部变量默认是`storage`, 并且状态变量必须是`storage`.
There is also a third data location, calldata, which is a non-modifiable, non-persistent area where function arguments are stored. Function parameters (not return parameters) of external functions are forced to calldata and behave mostly like memory.
第三种`数据存储位置`叫做`calldata`, 它是只读的, 临时的区域, 用来存储函数的参数.外部函数的参数被强制设置为`calldata`,并且看上去和`memory`一样.
Data locations are important because they change how assignments behave: assignments between storage and memory and also to a state variable (even from other state variables) always create an independent copy. Assignments to local storage variables only assign a reference though, and this reference always points to the state variable even if the latter is changed in the meantime. On the other hand, assignments from a memory stored reference type to another memory-stored reference type do not create a copy.
`数据存储位置`很重要, 因为它关系到改变和赋值的操作: `storage`和`memory`之间的赋值都会创建一个独立的copy; `storage`之间的赋值仅仅是引用传递, 所引用的对象后期可能会发生改变. 另一方面, 两个`memory`之间的赋值, 则不会创建新的copy.
Summary
-
Forced data location:
parameters (not return) of external functions: calldatastate variables: storage
-
Default data location:
parameters (also return) of functions: memoryall other local variables: storage
-
new出来的数组是
memory
//官方文档
pragma solidity ^0.4.0;
contract C {
uint[] x; // the data location of x is storage
// the data location of memoryArray is memory
function f(uint[] memoryArray) public {
x = memoryArray; // works, copies the whole array to storage
var y = x; // works, assigns a pointer, data location of y is storage
y[7]; // fine, returns the 8th element
y.length = 2; // fine, modifies x through y
delete x; // fine, clears the array, also modifies y
// The following does not work; it would need to create a new temporary /
// unnamed array in storage, but storage is "statically" allocated:
// y = memoryArray;
// This does not work either, since it would "reset" the pointer, but there
// is no sensible location it could point to.
// delete y;
g(x); // calls g, handing over a reference to x
h(x); // calls h and creates an independent, temporary copy in memory
}
function g(uint[] storage storageArray) internal {}
function h(uint[] memoryArray) public {}
}
测试代码
pragma solidity ^0.4.17;
contract Test{
uint[] public array ;
modifier initArray() {
delete array; //清空数组
array.push(1);
array.push(2);
_;
}
function test1() initArray public{
uint[] storage pArray = array; //引用
pArray[0] = 999;
}
function test2() initArray public{
uint[] memory newArray = array; //值传递, 相当于将array中的拷贝到一个新的数组中
newArray[0] = 444;
}
//-------------------------------------------------------
function test3() public initArray{
test4(array);
}
function test4(uint [] memArray) public{
array = memArray;
changeArray(array);
}
// 参数是storage类型时，函数必须是private或internal类型的
function changeArray(uint[] storage arrayTest) internal{
arrayTest[0] = 666;
}
//-------------------------------------------------------
}
智能合约效率问题
function approveRequest(uint nArrayIndex) public{
require(nArrayIndex < payRequests.length);
PayRequest storage request = payRequests[nArrayIndex];
//消耗大量gas
for(uint i = 0; i < addrPlayers.length; i++){
if(addrPlayers[i] == msg.sender) {
break;
}
if(i == addrPlayers.length - 1 /* && addrPlayers[i] != msg.sender*/){
require(false);
}
}
//消耗大量gas
for(i =0; i < request.vctVotedAddr.length; i++){
if(msg.sender == request.vctVotedAddr[i]){
require(false);
}
}
request.nAgreeCount += 1;
request.vctVotedAddr.push(msg.sender);
}
优化后
function approveRequest(uint nArrayIndex) public{
require(nArrayIndex < payRequests.length);
PayRequest storage request = payRequests[nArrayIndex];
require(mapPlayer[msg.sender]);
require(payRequests[nArrayIndex].mapVote[msg.sender] == false);
request.nAgreeCount += 1;
payRequests[nArrayIndex].mapVote[msg.sender] = true;
}
案例: 众筹
pragma solidity ^0.4.17;
//用智能合约部署智能合约
contract FundingFactory{
address[] public fundings;
function deploy(string _strProName, uint _nSupportMoney, uint _nGoalMoney) public{
address funding = new Funding(_strProName, _nSupportMoney , _nGoalMoney, msg.sender);
fundings.push(funding);
}
}
contract Funding{
bool bSuccessFlag = false;
address public addrManager;
string public strProjectName;
uint public nSupportMoney;
uint public nEndTime;
uint public nGoalMoney;
address [] public addrPlayers;
mapping(address=>bool) mapPlayer; //使用mapping提高效率, 降低gas消耗
PayRequest[] public payRequests; //付款请求结构体
struct PayRequest{
string strDesc;
uint nPayment; //out
address addrShop;
bool bCompleted;
mapping(address=>bool) mapVote;
//address[] vctVotedAddr;
uint nAgreeCount;
}
modifier onelyManager(){
//require(bSuccessFlag);
require(msg.sender == addrManager);
_;
}
function createRequest(string _strDesc, uint _nPayment, address _addrShop) public onelyManager{
PayRequest memory payRequest = PayRequest({
strDesc : _strDesc,
nPayment : _nPayment,
addrShop : _addrShop,
bCompleted : false,
nAgreeCount : 0
});
payRequests.push(payRequest);
}
function Funding(string _strProName, uint _nSupportMoney, uint _nGoalMoney, address _manager) public{
addrManager = _manager;//msg.sender;
strProjectName = _strProName;
nSupportMoney = _nSupportMoney;
nGoalMoney = _nGoalMoney;
nEndTime = now + 4 weeks;
}
function getBalance() view public returns(uint){
return this.balance;
}
function getPlayersCount()public view returns(uint){
return addrPlayers.length;
}
function getPlayers() public view returns(address[]){
return addrPlayers;
}
function getRemainSeconds() public view returns(uint){
return (nEndTime - now) ; //seconds
}
function checkStatus() view public{
require(bSuccessFlag == false);
require(now > nEndTime);
require(this.balance > nGoalMoney);
}
function support() payable public{
require(msg.value >= 50 wei);
nSupportMoney += msg.value;
addrPlayers.push(msg.sender);
mapPlayer[msg.sender] = true;
}
function approveRequest(uint nArrayIndex) public{
require(nArrayIndex < payRequests.length);
PayRequest storage request = payRequests[nArrayIndex];
require(mapPlayer[msg.sender]);
require(payRequests[nArrayIndex].mapVote[msg.sender] == false);
request.nAgreeCount += 1;
payRequests[nArrayIndex].mapVote[msg.sender] = true;
}
// function approveRequest(uint nArrayIndex) public{
// require(nArrayIndex < payRequests.length);
// PayRequest storage request = payRequests[nArrayIndex];
// for(uint i = 0; i < addrPlayers.length; i++){
// if(addrPlayers[i] == msg.sender) {
// break;
// }
// if(i == addrPlayers.length - 1 /* && addrPlayers[i] != msg.sender*/){
// require(false);
// }
// }
// for(i =0; i < request.vctVotedAddr.length; i++){
// if(msg.sender == request.vctVotedAddr[i]){
// require(false);
// }
// }
// request.nAgreeCount += 1;
// request.vctVotedAddr.push(msg.sender);
// }
function finilizeRequest(uint nRequestIndex) public{
PayRequest storage requst = payRequests[nRequestIndex];
require(requst.bCompleted == false);
require(requst.nAgreeCount * 2 > addrPlayers.length);
//付款
require(this.balance > requst.nPayment);
requst.addrShop.transfer(requst.nPayment);
requst.bCompleted = true;
}
}
