Solidity 入門

Ming-der Wang, twitter @mingderwang

ming@Log4Analytics.com

11/26/2016 9:30-12am

Blockchain Summit 2016, Taipei

王銘德

Taipei Ethereum

Taipei Ethereum Meetup 社團

以色龍 Ethereum 臉書

ethertw.slack.com 討論區

那什麼是 "智能合約"？ - Smart Contracts

如何在 Ethereum 網路上開發應用?

也就是寫一個所謂的"智能合約“

注意! 它名字取的不好 (既沒有A.I. 也沒有法律效用)

什麼東西可以寫成或利用智能合約

一件事需要有 trust (“相信") 的時候
需要公開透明, 卻又不能篡改的東西 (比如說, 歷史? No!)
你跟政府有簽合約嗎? 你為何相信政府的鈔票? (美金呢?)

例如：

眾籌募資: Digix , WeiFund, TheDAO (名字取的不好, 被"盜“了約 12 億台幣)
選舉, 選委員, 民主投票, 公證, 契約...
網路樂透, 紅利點數
想些超大的應用? 你生活周遭發生的事, 能用智能合約來解決嗎?
其他... (請發揮您最豐富的想像力)

Solidity

一種最常用的智能合約程式語言

類似 Javascript, 但不是 Javascript
可以編譯成 bytecode 在 Ethereum VM 上執行
程式只能在 blockchain 測試和執行
無需主機, 程式永遠存在(理論上)
須透過 Ethereum-Wallet (Mist) 或 Parity browser 來部署

開發環境

你至少要安裝一個 Ethereum Wallet
程式編輯與編譯, 可以用網路版
或用你最喜歡的編輯器 vim 也行
最高竿的直接用 web3.js 在 Chrome debugger 裡用 CLI 指令集直接執行也行.
也可用 devtool 介面

Ethereum Wallet

Solidity Realtime Compiler

Chrome devtool

Solidity 語言特性

它也是物件導向程式語言
除了 float 以外, 有各種 types
也有 structs 結構
有 mappings (a kind of arrays)
有 arrays
有一個 address 特殊 object
data location 資料放哪?
有 functions and exceptions
說明文件 (英文) 還算清楚

Mortal

contract mortal {
address owner;
function mortal() {

owner = msg.sender; }

function kill() {

if (msg.sender == owner)

     selfdestruct(owner);    }
}

HelloWorld

contract helloworld is mortal {

/* helloworld 就會繼承了 mortal 的 kill 功能*/

string storeData;

function set(string x) {
storeData = x; }

function get() constant returns (string data) {
return storeData; }

}

物件導向 - 繼承

格式 (type)

bool

int8, int16, int24 ... int256

uint8, uint16, ... uint256

uint and int are aliases for uint256 and int256,

address

string

bytes1, bytes2, bytes3, ..., bytes32.

byte is an alias for bytes1

結構 (struct)

 struct Funder {
    address addr;
    uint amount;
  }

目前不支援浮點運算 float

Explicit Conv.

int8 y = -3;
uint x = uint(y);

Type Deduction

uint20 x = 0x123;
var y = x;

// y will be unit20 too

uint32 a = 0x12345678;
uint16 b = uint16(a); 
// b will be 0x5678 now

The type is only deduced from the first assignment, so the loop in the following snippet is infinite, as i will have the type uint8 and any value of this type is smaller than 2000. for (var i = 0; i < 2000; i++) { ... }

mappings

Mapping types are declared as mapping (_KeyType => _ValueType), where _KeyType can be almost any type except for a mapping and _ValueType can actually be any type, including mappings.
Mappings are only allowed for state variables (or as storage reference types in internal functions).
no length

contract MyToken { /* This creates an array with all balances */

mapping (address => uint256) public balanceOf;

function MyToken() {
balanceOf[msg.sender] = 21000000; }

}

Arrays

contract C {
  function f(uint len) {
    uint[] memory a = new uint[](7);
    bytes memory b = new bytes(len);// memory
    // Here we have a.length == 7 and b.length == len
    a[6] = 8;
  }
}

An array of fixed size k and element type T is written as T[k], an array of dynamic size as T[].

Functions and Exceptions

contract Sharer {
    function sendHalf(address addr) returns (uint balance) {
        if (!addr.send(msg.value/2))
            throw; // also reverts the transfer to Sharer
        return this.balance;
    }
}

address' Methods

address holds a 20 byte value (size of an Ethereum address). Address types also have members, like send()

address x = 0x123;
address myAddress = this;
if (x.balance < 10 && myAddress.balance >= 10) x.send(10);

All contracts inherit the members of address, so it is possible to query the balance of the current contract using this.balance.

if the address is a contract

address nameReg = 0x72ba7d8e73fe8eb666ea66babc8116a41bfb10e2;
nameReg.call("register", "MyName");
nameReg.call(bytes4(sha3("fun(uint256)")), a);

call returns a boolean indicating whether the invoked function terminated (true) or caused an EVM exception (false).
delegatecall is to use library code which is stored in another contract.
callcode was available that did not provide access to the original msg.sender and msg.value values.

如何讓別人執行你的Contract

[ { "constant": false, "inputs": [], "name": "kill", "outputs": [], "type": "function" }, { "constant": false, "inputs": [ { "name": "x", "type": "string" } ], "name": "set", "outputs": [], "type": "function" }, { "constant": true, "inputs": [], "name": "get", "outputs": [ { "name": "data", "type": "string", "value": "hello CCLiang" } ], "type": "function" } ]

跟你的 Contract Address