於terminal輸入：
find . -name .DS_Store -print0 | xargs -0 git rm -f --ignore-unmatch
輸入以下指令將.DS_Store加入.gitignore
echo .DS_Store >> .gitignore
commit .gitignore file
git add .gitignore
git commit -m '.DS_Store banished!'
“Be your own bank”
整個Bitcoin全節點可以視作一種純P2P網路，為了保持各個節點間資料一致性，傳播資料要考慮有假造的節點，如何確保資料同步、一致性，形成共識？–>要對抗女巫攻擊(惡意使壞的節點)
考慮視域變化(view-change)，分為三階段：
有時候分岔不是因為技術、惡意節點、駭客，而是因為社群意見的分裂。
以下兩種跟軟體升級、程式碼或協定更動有關
Initial Coin Offering(ICO) Initial Exchange Offering(IEO) Initial Fork Offering(IFO) Security Token Offering(STO)
// SPDX-License-Identifier: MIT
Variables whose values are permanently stored in contract storage.
constant 或 immutable.
constant : The value has to be fixed at compile-time/ It is also possible to define constant variables at the file level.immutable : It can still be assigned at construction time.bool : 包括constants true and falseint / unitfixed / ufixedaddress: Holds a 20 byte value (size of an Ethereum address).address payable: Same as address, but with the additional members transfer and send.可以接收Ether.address payablebalance and transfer
address payable x = payable(0x123);
address myAddress = address(this);
if (x.balance < 10 && myAddress.balance >= 10) x.transfer(10);
call, delegatecall and staticcalladdress(this).balance.bytes1, bytes2, bytes3, …, bytes32 hold a sequence of bytes from one to up to 32.bytes,string Not a value-type!"foo" "bar" is equivalent to "foobar" –>遇到超長string的時候有用type(NameOfEnum).min and type(NameOfEnum).max you can get the smallest and respectively largest value of the given enum.memorystoragecalldata
// SPDX-License-Identifier: GPL-3.0
pragma solidity >=0.5.0 <0.9.0;
contract C {
// The data location of x is storage.
// This is the only place where the
// data location can be omitted.
uint[] x;
// The data location of memoryArray is memory.
function f(uint[] memory memoryArray) public {
x = memoryArray; // works, copies the whole array to storage
uint[] storage y = x; // works, assigns a pointer, data location of y is storage
y[7]; // fine, returns the 8th element
y.pop(); // 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) internal pure {}
function h(uint[] memory) public pure {}
}
uint[][5] –> 和其他語言相反
uint[][5] memory x 後
* access the seventh uint in the third dynamic array using x[2][6]
* access the third dynamic array, usex[2]X[3] is always an array containing three elements of type X, even if X is itself an array –> 和其他語言不同uint[] memory a = new uint[](7);.push member functions are not available)[1, 2, 3] is uint8[3] memory, because the type of each of these constants is uint8. If you want the result to be a uint[3] memory type, you need to convert the first element to uint. ex. [uint(1), 2, 3][1, -1] is invalid，因為第一個是uint8，而第二個是int8，應該寫成[int8(1), -1]uint[] memory x = [uint(1), 3, 4]; –>錯 uint[] memory x = new uint[](3);
x[0] = 1;
x[1] = 3;
x[2] = 4;
bytesstringmapping(_KeyType => _ValueType) _VariableName
keccak256 hash is used to look up the value. 所以對key沒有長度的限制bytes, string, or any contract or enum type. Other user-defined or complex types, such as mappings, structs or array types are not allowed.delete a assigns the initial value for the type to a.
uint x = data;
delete x; // sets x to 0, does not affect data
delete data; // sets data to 0, does not affect x
uint[] storage y = dataArray;
delete dataArray; // this sets dataArray.length to zero, but as uint[] is a complex object, also
// y is affected which is an alias to the storage object
// On the other hand: "delete y" is not valid, as assignments to local variables
// referencing storage objects can only be made from existing storage objects.
function (<parameter types>) {internal|external} [pure|constant|view|payable] [returns (<return types>)]
| 預設：internal，所以internal | external可省略 |
.address returns the address of the contract of the function..selector returns the ABI function selector{gas: ...} and {value: ...} to specify the amount of gas or the amount of wei sent to a function, respectively.f() does not work, but this.f() works).
Functions can be declared view in which case they promise not to modify the state. 下面行為被認為是 modifying the state:
Functions can be declared pure in which case they promise not to read from or modify the state. 下面行為被認為是reading from the state:
讓函式可以接收以太幣 延伸閱讀
receive() external payable { ... }
* 不用function keyword
* 不能有arguments
* 不能return東西
*一定要有external visibility and payable state mutability
fallback () external [payable] or
fallback (bytes calldata _input) external [payable] returns (bytes memory _output)
* 不用function keyword
* 不能有arguments
* 不能return東西
*一定要有external visibilityassert function creates an error of type Panic(uint256).require function either creates an error without any data or an error of type Error(string).revert statement takes a custom error as direct argument without parentheses:
revert CustomError(arg1, arg2);// SPDX-License-Identifier: GPL-3.0
pragma solidity >=0.8.1;
interface DataFeed { function getData(address token) external returns (uint value); }
contract FeedConsumer {
DataFeed feed;
uint errorCount;
function rate(address token) public returns (uint value, bool success) {
// Permanently disable the mechanism if there are
// more than 10 errors.
require(errorCount < 10);
try feed.getData(token) returns (uint v) {
return (v, true);
} catch Error(string memory /*reason*/) {
// This is executed in case
// revert was called inside getData
// and a reason string was provided.
errorCount++;
return (0, false);
} catch Panic(uint /*errorCode*/) {
// This is executed in case of a panic,
// i.e. a serious error like division by zero
// or overflow. The error code can be used
// to determine the kind of error.
errorCount++;
return (0, false);
} catch (bytes memory /*lowLevelData*/) {
// This is executed in case revert() was used.
errorCount++;
return (0, false);
}
}
}
參考網址
The only way to remove code from the blockchain is when a contract at that address performs the selfdestruct operation.
很危險！如果其他人傳送Ether到已經被移除的合約地址，Ether會被永久遺失。