以太坊 （四）十分钟帮你彻底走上智能合约开发之路

学习目标

  1. 了解智能合约
  2. 简单环境搭建
  3. 能够利用solidity编写Hello World合约
  4. 合约部署
  5. 和合约互动

智能合约是什么

在区块链上运行的程序，通常称为智能合约（Smart Contract）。所以通常会把写区块链程序改称写智能合约。虽然比特币（Bitcoin）上也能写智能合约，但是比特币所支持的语法仅与交易有关，能做的事情比较有限。因此目前提到写智能合约，通常指的是支持执行图灵完备程序的以太坊（Ethereum）区块链 。

智能合约的应用场景

目前最常见的智能合约是各种加密货币合约，开发者可以很容易地透过部署一个智能合约，来提供运行于以太坊上的新加密代币。如果这份智能合约相容于 ERC20 标准 1，开发者不需要重新开发从挖矿到交易的整个代币生态系，你的新加密代币就可以直接使用支持支持以太坊的电子钱包来收送，大大降低了建立新加密代币的门槛。

智能合约也可以用来运作各种公开公正的自动服务机构（DAO，权力下放自治组织）。透过分散在全球各节点上运作的智能合约，所有运作与决策都是公开透明的，降低了交易的不确定性（不确定性）。

如何编写智能合约？

Ethereum上的智能合约需要使用solidity语言来编写。官方宣传上说solidity是一种类似的JavaScript的语言，而且围绕着JavaScript的各种开发工具链都是使用属于使用 Javascript 生态系的 NPM 来提供的。

将智能合约部署到区块链的流程

写好solidity代码（.sol）后，需要先将程序代码编译（编译）成 EVM（Ethereum Virtual Machine）能读懂的二进制度Contract ByteCode，才能部署到 Ethereum 的区块链上执行。部署到区块链上的合约会有一个和钱包地址（地址）一样格式的合约地址（Contract Address）。

Snip20170918_10.png

部署后智能合约可自动执行。后续呼叫智能合约的时候，使用者可以使用部署合约的钱包地址（所有者帐户），或依据编写的智能合约条件，让其他钱包地址也能呼叫这个智能合约。 呼叫智能合约，其实就是向这个合约地址发起交易，只是交易的不只是代币，而可以是智能合约提供的呼叫方法。

Snip20170918_11.png

开发所需工具

  • 以太坊内存块链测试环境ganache-cli
  • 智能合约开发框架truffle
  • 编辑器Atom搭配solidity插件

开发工具安装

首先开发机上必须装好 Node.js，再使用以下命令安装ganache-cli和truffle：

$  npm install -g ganache-cli truffle

注意：如果安装过程中遇到问题，可以升级下node的版本试试。

Atom下载安装，安装solidity相关插件

tom.png

启动 ganache-cli

安装好后随时可以使用ganache-cli命令来启动以太坊测试环境。

wangsanjundeMacBook-Pro:~ wangsanjun$ ganache-cli
Ganache CLI v6.0.3 (ganache-core: 2.0.2)

Available Accounts
==================
(0) 0xde12463cc19e098ba773adfd236fedb0b21faeb6
(1) 0xdfd59924386b19ad1cfea2088c3279363d2fc936
(2) 0xa19c5064e75fee1dad8bdeb9f4e7a373ce3fa1f7
(3) 0x53d5e0b93659bd7f7f7263365c031e318b2261c0
(4) 0x06b6da8c19b3a0f770f57fe5f6ff469d95ebe098
(5) 0x78121378f88cc8295255f65822e0da64829d1464
(6) 0xf2e3eb6669a941d7ad0984d0fa1e8b88ea6eab3d
(7) 0x39400e42b45691b8ad06507e80f644976d512db7
(8) 0x52c644f97806cf3371150561dd1a44e768378d11
(9) 0xf30705a7669c67d96f80288018e7993918ca62d6

Private Keys
==================
(0) 71a96e34a8bd71f2380bc0b46f62109f0c460afc469ab02c7a89374dba107223
(1) 8ec9ab82818b47eea746d0be5a75c159a21107422ee2624a6b8427bdf0e837d0
(2) c50a555a76aa502805da94b6facac4b3784965f10e57218f23704f4d8526a7ed
(3) 81088a0a92e8898c455b607080b0b82e78033b5728494df98ed2a06d1e7ab323
(4) 21b347c449c0e7571fd6f82ef6feea881a56e9d6c172c0134316036fabe6ccdc
(5) 0498c47475049e0c8799593b063ff2e0ee5f07e9fb6d4db05a9d57adc4b9bc23
(6) 4528f26f7fdc64c54d12c32dad9c1836155ef8fadce316bc351ffd47fbcdb6fa
(7) 371eb0e4f309117d53d10c007550acb19c1a387f9e034a52f3e741b8d955fe3c
(8) 4d65400d1f12bf2bb26189e8beadec98bb34e85e34db33ee969449e4993c2b2c
(9) 160a3031008a3583f9cacfe3aebf34a5bc0cbc4c0556cda97baa32c90ea92859

HD Wallet
==================
Mnemonic:      creek found enroll warm flame door used essay indoor cry carpet journey
Base HD Path:  m/44'/60'/0'/0/{account_index}

Listening on localhost:8545

可以看到ganache-cli启动后自动建立了10个帐号（Accounts），与每个帐号对应的私钥（Private Key）。每个帐号中都有100个测试用的以太币（Ether）。要注意ganache-cli仅运行在內存中，因此每次重开时都会回到全新的状态。

建立项目

开启另一个终端窗口，输入以下命令以建立项目：

wangsanjundeMacBook-Pro:Desktop wangsanjun$ mkdir SmartContractDemo
wangsanjundeMacBook-Pro:Desktop wangsanjun$ cd SmartContractDemo/
wangsanjundeMacBook-Pro:SmartContractDemo wangsanjun$ ls
wangsanjundeMacBook-Pro:SmartContractDemo wangsanjun$ mkdir HelloWorld
wangsanjundeMacBook-Pro:SmartContractDemo wangsanjun$ cd HelloWorld/
wangsanjundeMacBook-Pro:HelloWorld wangsanjun$ ls
wangsanjundeMacBook-Pro:HelloWorld wangsanjun$ truffle init
Downloading...
Unpacking...
Setting up...
Unbox successful. Sweet!

Commands:

  Compile:        truffle compile
  Migrate:        truffle migrate
  Test contracts: truffle test

目录结构：

truffle项目目录结构.png

  • /contracts:存放智能合约原始代码的地方，可以看到里面已经有一个sol文件，我们开发的HelloWorld.sol文件就存放在这个文件夹。

    wangsanjundeMacBook-Pro:HelloWorld wangsanjun$ cd contracts/
wangsanjundeMacBook-Pro:contracts wangsanjun$ ls
Migrations.sol

  • /migrations:这是 Truffle用来部署智能合约的功能，待会儿我们会新建一个类似1_initial_migration.js的文件来部署 HelloWorld.sol。

    wangsanjundeMacBook-Pro:HelloWorld wangsanjun$ cd migrations/
wangsanjundeMacBook-Pro:migrations wangsanjun$ ls
1_initial_migration.js

  • /test:测试智能合约的代码放在这里，支持js 与 sol 测试。

  • truffle.js／truffle-config.js: Truffle 的配置文件,需要配置要连接的以太坊网络

image

新建 HelloWorld 合约

在contracts文件夹下新建HelloWorld.sol文件

HelloWorld.sol文件內容如下：

pragma solidity ^0.4.17;
contract HelloWorld {
  function sayHello() returns (string) {
    return "HelloWorld";
  }
}

讲解

pragma solidity ^0.4.17;

第一行指的是目前使用的solidity版本，不同版本的solidity可能会编译出不同的bytecode。^代表兼容solidity``0.4.17 ~ 0.4.9的版本。

contract HelloWorld {
    ...
}

contract关键字类似于其他语言中较常见的class。因为solidity是专为智能合约（Contact）设计的语言，声明contract后即内置了开发智能合约所需的功能。也可以把这句理解为class HelloWorld extends Contract。

 function sayHello() returns (string) {
    return "HelloWorld";
  }

函数的结构与其他程序类似，但如果有传入的参数或回传值，需要指定参数或回传值的类型（type）。

编译

现在执行truffle compile命令，我们可以将HelloWorld.sol原始码编译成Ethereum bytecode。

wangsanjundeMacBook-Pro:HelloWorld wangsanjun$ truffle compile
Compiling ./contracts/HelloWorld.sol...
Compiling ./contracts/Migrations.sol...

Compilation warnings encountered:

/Users/wangsanjun/Desktop/SmartContractDemo/HelloWorld/contracts/HelloWorld.sol:3:3: Warning: No visibility specified. Defaulting to "public".
  function sayHello() returns (string) {
  ^
Spanning multiple lines.
,/Users/wangsanjun/Desktop/SmartContractDemo/HelloWorld/contracts/HelloWorld.sol:3:3: Warning: Function state mutability can be restricted to pure
  function sayHello() returns (string) {
  ^
Spanning multiple lines.

Writing artifacts to ./build/contracts

wangsanjundeMacBook-Pro:HelloWorld wangsanjun$ cd build
wangsanjundeMacBook-Pro:build wangsanjun$ ls
contracts
wangsanjundeMacBook-Pro:build wangsanjun$ cd contracts/
wangsanjundeMacBook-Pro:contracts wangsanjun$ ls
HelloWorld.json Migrations.json
编译成功.png

Warning暂时忽略，编译成功后，会在HelloWorld文件夹下面的build/contracts文件夹下面看见HelloWorld.json文件。

部署

truffle框架中提供了方便部署合约的脚本。新建migrations/2_deploy_contracts.js文件（脚本使用Javascript编写），将内容修改如下：

var HelloWorld = artifacts.require("HelloWorld");
module.exports = function(deployer) {
  deployer.deploy(HelloWorld);
};
部署文件.png

使用artifacts.require语句来取得准备部署的合约。使用deployer.deploy语句将合约部署到区块链上。这边HelloWorld是contract的名称而不是文件名。因此可以用此语法读入任一.sol文件中的任一合约。

现在执行truffle migrate命令：

wangsanjundeMacBook-Pro:HelloWorld wangsanjun$ truffle migrate
Error: No network specified. Cannot determine current network.
    at Object.detect (/Users/wangsanjun/.nvm/versions/node/v7.10.1/lib/node_modules/truffle/build/webpack:/~/truffle-core/lib/environment.js:31:1)
    at /Users/wangsanjun/.nvm/versions/node/v7.10.1/lib/node_modules/truffle/build/webpack:/~/truffle-core/lib/commands/migrate.js:91:1
    at finished (/Users/wangsanjun/.nvm/versions/node/v7.10.1/lib/node_modules/truffle/build/webpack:/~/truffle-workflow-compile/index.js:53:1)
    at /Users/wangsanjun/.nvm/versions/node/v7.10.1/lib/node_modules/truffle/build/webpack:/~/truffle-compile/index.js:303:1
    at /Users/wangsanjun/.nvm/versions/node/v7.10.1/lib/node_modules/truffle/build/webpack:/~/truffle-compile/profiler.js:157:1
    at /Users/wangsanjun/.nvm/versions/node/v7.10.1/lib/node_modules/truffle/build/webpack:/~/truffle-compile/~/async/dist/async.js:3874:1
    at /Users/wangsanjun/.nvm/versions/node/v7.10.1/lib/node_modules/truffle/build/webpack:/~/truffle-compile/~/async/dist/async.js:473:1
    at replenish (/Users/wangsanjun/.nvm/versions/node/v7.10.1/lib/node_modules/truffle/build/webpack:/~/truffle-compile/~/async/dist/async.js:993:1)
    at iterateeCallback (/Users/wangsanjun/.nvm/versions/node/v7.10.1/lib/node_modules/truffle/build/webpack:/~/truffle-compile/~/async/dist/async.js:983:1)
    at /Users/wangsanjun/.nvm/versions/node/v7.10.1/lib/node_modules/truffle/build/webpack:/~/truffle-compile/~/async/dist/async.js:958:1
    at /Users/wangsanjun/.nvm/versions/node/v7.10.1/lib/node_modules/truffle/build/webpack:/~/truffle-compile/~/async/dist/async.js:3871:1
    at /Users/wangsanjun/.nvm/versions/node/v7.10.1/lib/node_modules/truffle/build/webpack:/~/truffle-compile/profiler.js:153:1
    at /Users/wangsanjun/.nvm/versions/node/v7.10.1/lib/node_modules/truffle/build/webpack:/~/truffle-compile/~/async/dist/async.js:1126:1
    at /Users/wangsanjun/.nvm/versions/node/v7.10.1/lib/node_modules/truffle/build/webpack:/~/truffle-compile/~/async/dist/async.js:473:1
    at iteratorCallback (/Users/wangsanjun/.nvm/versions/node/v7.10.1/lib/node_modules/truffle/build/webpack:/~/truffle-compile/~/async/dist/async.js:1050:1)
    at /Users/wangsanjun/.nvm/versions/node/v7.10.1/lib/node_modules/truffle/build/webpack:/~/truffle-compile/~/async/dist/async.js:958:1
    at /Users/wangsanjun/.nvm/versions/node/v7.10.1/lib/node_modules/truffle/build/webpack:/~/truffle-compile/~/async/dist/async.js:1123:1
    at /Users/wangsanjun/.nvm/versions/node/v7.10.1/lib/node_modules/truffle/build/webpack:/~/truffle-compile/profiler.js:132:1
    at FSReqWrap.oncomplete (fs.js:114:15)

报错了，Error: No network specified. Cannot determine current network.哦，原来找不到我们的私有链网络。也是啊，怎么着才能连接到我们本地的ganache-cli测试环境呢。原来需要配置truffle.js文件

module.exports = {
  networks: {
    development: {
      host: "127.0.0.1",
      port: 8545,
      network_id: "*" // Match any network id
    }
  }
};

重新执行truffle migrate命令：

wangsanjundeMacBook-Pro:HelloWorld wangsanjun$ truffle migrate
Using network 'development'.

Running migration: 1_initial_migration.js
  Deploying Migrations...
  ... 0xb821e6898642eac825b02a571f8ce4a3e0d0443e49274bbc4c70971a5ddea5c4
  Migrations: 0xb414c2a65d595dcae17c5c0c51076b95c8babd73
Saving successful migration to network...
  ... 0xd67eafbab4a191dbd18d70b7065f4857374d4770cdd4c44e6fb4f0a13dc27ce3
Saving artifacts...
Running migration: 2_deploy_contracts.js
  Deploying HelloWorld...
  ... 0x5f278a700ea1d9f5f9565841a621d9f4878184c43deb6819f7217435528c7bde
  HelloWorld: 0x046692c66a173925b95e378349433222e7a139bb
Saving successful migration to network...
  ... 0x02f4e867c23a4e21a850935f4642d5a2c5c2b195ce35ac0ba2e0cbda8c0f9a86
Saving artifacts...

如此一来合约已经部署到ganache-cli中。切换到ganache-cli窗口，可以看到ganache-cli有反应了。

ganache.png

与合约互动

truffle提供命令行工具，执行truffle console命令后，可用Javascript来和刚刚部署的合约互动。

truffle(development)> let contract;
undefined
truffle(development)> HelloWorld.deployed().then(instance => contract = instance)
TruffleContract {
  constructor: 
   { [Function: TruffleContract]
     _static_methods: 
      { setProvider: [Function: setProvider],
        new: [Function: new],
        at: [Function: at],
        deployed: [Function: deployed],
        defaults: [Function: defaults],
        hasNetwork: [Function: hasNetwork],
        isDeployed: [Function: isDeployed],
        detectNetwork: [Function: detectNetwork],
        setNetwork: [Function: setNetwork],
        resetAddress: [Function: resetAddress],
        link: [Function: link],
        clone: [Function: clone],
        addProp: [Function: addProp],
        toJSON: [Function: toJSON] },
     _properties: 
      { contract_name: [Object],
        contractName: [Object],
        abi: [Object],
        network: [Function: network],
        networks: [Function: networks],
        address: [Object],
        transactionHash: [Object],
        links: [Function: links],
        events: [Function: events],
        binary: [Function: binary],
        deployedBinary: [Function: deployedBinary],
        unlinked_binary: [Object],
        bytecode: [Object],
        deployedBytecode: [Object],
        sourceMap: [Object],
        deployedSourceMap: [Object],
        source: [Object],
        sourcePath: [Object],
        legacyAST: [Object],
        ast: [Object],
        compiler: [Object],
        schema_version: [Function: schema_version],
        schemaVersion: [Function: schemaVersion],
        updated_at: [Function: updated_at],
        updatedAt: [Function: updatedAt] },
     _property_values: {},
     _json: 
      { contractName: 'HelloWorld',
        abi: [Object],
        bytecode: '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',
        deployedBytecode: '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',
        sourceMap: '25:93:0:-;;;;;;;;;;;;;;;;;',
        deployedSourceMap: '25:93:0:-;;;;;;;;;;;;;;;;;;;;;;;;49:67;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;23:1:-1;8:100;33:3;30:1;27:2;8:100;;;99:1;94:3;90;84:5;80:1;75:3;71;64:6;52:2;49:1;45:3;40:15;;8:100;;;12:14;3:109;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;49:67:0;78:6;;:::i;:::-;92:19;;;;;;;;;;;;;;;;;;;;49:67;:::o;25:93::-;;;;;;;;;;;;;;;:::o',
        source: 'pragma solidity ^0.4.17;\ncontract HelloWorld {\n  function sayHello() returns (string) {\n    return "HelloWorld";\n  }\n}\n',
        sourcePath: '/Users/wangsanjun/Desktop/SmartContractDemo/HelloWorld/contracts/HelloWorld.sol',
        ast: [Object],
        legacyAST: [Object],
        compiler: [Object],
        networks: [Object],
        schemaVersion: '2.0.0',
        updatedAt: '2018-03-09T00:54:30.721Z' },
     setProvider: [Function: bound setProvider],
     new: [Function: bound new],
     at: [Function: bound at],
     deployed: [Function: bound deployed],
     defaults: [Function: bound defaults],
     hasNetwork: [Function: bound hasNetwork],
     isDeployed: [Function: bound isDeployed],
     detectNetwork: [Function: bound detectNetwork],
     setNetwork: [Function: bound setNetwork],
     resetAddress: [Function: bound resetAddress],
     link: [Function: bound link],
     clone: [Function: bound clone],
     addProp: [Function: bound addProp],
     toJSON: [Function: bound toJSON],
     web3: 
      Web3 {
        _requestManager: [Object],
        currentProvider: [Object],
        eth: [Object],
        db: [Object],
        shh: [Object],
        net: [Object],
        personal: [Object],
        bzz: [Object],
        settings: [Object],
        version: [Object],
        providers: [Object],
        _extend: [Object] },
     class_defaults: 
      { from: '0x4068364a85fa3bac7e83c45581397fe9c5111b39',
        gas: 6721975,
        gasPrice: 100000000000 },
     currentProvider: 
      HttpProvider {
        host: 'http://127.0.0.1:8545',
        timeout: 0,
        user: undefined,
        password: undefined,
        headers: undefined,
        send: [Function],
        sendAsync: [Function],
        _alreadyWrapped: true },
     network_id: '1520386125068' },
  abi: 
   [ { constant: false,
       inputs: [],
       name: 'sayHello',
       outputs: [Object],
       payable: false,
       stateMutability: 'nonpayable',
       type: 'function' } ],
  contract: 
   Contract {
     _eth: 
      Eth {
        _requestManager: [Object],
        getBalance: [Object],
        getStorageAt: [Object],
        getCode: [Object],
        getBlock: [Object],
        getUncle: [Object],
        getCompilers: [Object],
        getBlockTransactionCount: [Object],
        getBlockUncleCount: [Object],
        getTransaction: [Object],
        getTransactionFromBlock: [Object],
        getTransactionReceipt: [Object],
        getTransactionCount: [Object],
        call: [Object],
        estimateGas: [Object],
        sendRawTransaction: [Object],
        signTransaction: [Object],
        sendTransaction: [Object],
        sign: [Object],
        compile: [Object],
        submitWork: [Object],
        getWork: [Object],
        coinbase: [Getter],
        getCoinbase: [Object],
        mining: [Getter],
        getMining: [Object],
        hashrate: [Getter],
        getHashrate: [Object],
        syncing: [Getter],
        getSyncing: [Object],
        gasPrice: [Getter],
        getGasPrice: [Object],
        accounts: [Getter],
        getAccounts: [Object],
        blockNumber: [Getter],
        getBlockNumber: [Object],
        protocolVersion: [Getter],
        getProtocolVersion: [Object],
        iban: [Object],
        sendIBANTransaction: [Function: bound transfer] },
     transactionHash: null,
     address: '0x046692c66a173925b95e378349433222e7a139bb',
     abi: [ [Object] ],
     sayHello: 
      { [Function: bound ]
        request: [Function: bound ],
        call: [Function: bound ],
        sendTransaction: [Function: bound ],
        estimateGas: [Function: bound ],
        getData: [Function: bound ],
        '': [Circular] },
     allEvents: [Function: bound ] },
  sayHello: 
   { [Function]
     call: [Function],
     sendTransaction: [Function],
     request: [Function: bound ],
     estimateGas: [Function] },
  sendTransaction: [Function],
  send: [Function],
  allEvents: [Function: bound ],
  address: '0x046692c66a173925b95e378349433222e7a139bb',
  transactionHash: null }

truffle(development)> contract.sayHello.call()
'Hello World'

讲解

HelloWorld.deployed().then(instance => contract = instance)

truffle console中预载了truffle-contract函数库，以方便操作部署到区块链上的合约。

这边使用HelloWorld.deployed().then语句来取得HelloWorld合约的Instance（实例），并存到contract变量中，以方便后续的调用。

上面用的是Javascript ES6+的语法，这句也可以写成：

HelloWorld.deployed().then(instance => {
    contract = instance
});

还可以用 ES5 的写法：

HelloWorld.deployed().then(function(instance) {
  hello = instance;
});

truffle(development)> contract.sayHello.call()
'Hello World'

如此一来，我们已写好并部署完成了第一个智能合约，也验证了合约确实可以运作。

加入新方法

我们在HelloWorld.sol中再加入一个echo方法，echo方法接受输入一个参数，并回传传送的参数。

function echo(string name) constant returns (string) {
    return name;
}

新的echo方法中传入了一个name参数。我们也为echo方法加入一个constant声明，表示调用这个方法并不会改变区块链的状态。如此一来，透过truffle-contract来调用此方法时，会自动选用call来呼叫，也不需要额外提供 gas。

由于更新了合约内容，我们需要先重新新编译一次，将编译结果部署到ganache-cli上，再透过truffle console执行看看结果。

wangsanjundeMacBook-Pro:HelloWorld wangsanjun$ truffle compile
Compiling ./contracts/HelloWorld.sol...

Compilation warnings encountered:

/Users/wangsanjun/Desktop/SmartContractDemo/HelloWorld/contracts/HelloWorld.sol:3:3: Warning: No visibility specified. Defaulting to "public".
  function sayHello() returns (string) {
  ^
Spanning multiple lines.
,/Users/wangsanjun/Desktop/SmartContractDemo/HelloWorld/contracts/HelloWorld.sol:7:3: Warning: No visibility specified. Defaulting to "public".
  function echo(string name) constant returns (string) {
  ^
Spanning multiple lines.
,/Users/wangsanjun/Desktop/SmartContractDemo/HelloWorld/contracts/HelloWorld.sol:3:3: Warning: Function state mutability can be restricted to pure
  function sayHello() returns (string) {
  ^
Spanning multiple lines.
,/Users/wangsanjun/Desktop/SmartContractDemo/HelloWorld/contracts/HelloWorld.sol:7:3: Warning: Function state mutability can be restricted to pure
  function echo(string name) constant returns (string) {
  ^
Spanning multiple lines.

Writing artifacts to ./build/contracts

wangsanjundeMacBook-Pro:HelloWorld wangsanjun$ truffle migrate --reset
Using network 'development'.

Running migration: 1_initial_migration.js
  Replacing Migrations...
  ... 0x9f104e49cbee7b4d058109400529078162b180f402e23b9ff237157a1599a019
  Migrations: 0x95fa54d8abaf328c0d0c2c6713c369feb0eda7fe
Saving successful migration to network...
  ... 0x069eb545ba8689dfd9ea76d4160b47c37f7c6bb7a8bd91f4f7d7ee3d45e2c85c
Saving artifacts...
Running migration: 2_deploy_contracts.js
  Replacing HelloWorld...
  ... 0x8a2d20fb9009bd631e602ede2605bf1b7e750ec81569bdd202e2379e276f05ad
  HelloWorld: 0xb49e482f7b9201d5305e2d6a1bf1bad3d4c05540
Saving successful migration to network...
  ... 0x70a4b9f5234b2bfc67f70ccd1722b1256a9b1587079dd7aca54c957f40c00443
Saving artifacts...

wangsanjundeMacBook-Pro:HelloWorld wangsanjun$ truffle console
truffle(development)> let contract;
undefined
truffle(development)> HelloWorld.deployed().then(intance => contract = instance) 
ReferenceError: instance is not defined
    at HelloWorld.deployed.then.intance (evalmachine.<anonymous>:1:50)
    at process._tickDomainCallback (internal/process/next_tick.js:135:7)
truffle(development)> HelloWorld.deployed().then(instance => contract = instance)
TruffleContract {
  constructor: 
   { [Function: TruffleContract]
     _static_methods: 
      { setProvider: [Function: setProvider],
        new: [Function: new],
        at: [Function: at],
        deployed: [Function: deployed],
        defaults: [Function: defaults],
        hasNetwork: [Function: hasNetwork],
        isDeployed: [Function: isDeployed],
        detectNetwork: [Function: detectNetwork],
        setNetwork: [Function: setNetwork],
        resetAddress: [Function: resetAddress],
        link: [Function: link],
        clone: [Function: clone],
        addProp: [Function: addProp],
        toJSON: [Function: toJSON] },
     _properties: 
      { contract_name: [Object],
        contractName: [Object],
        abi: [Object],
        network: [Function: network],
        networks: [Function: networks],
        address: [Object],
        transactionHash: [Object],
        links: [Function: links],
        events: [Function: events],
        binary: [Function: binary],
        deployedBinary: [Function: deployedBinary],
        unlinked_binary: [Object],
        bytecode: [Object],
        deployedBytecode: [Object],
        sourceMap: [Object],
        deployedSourceMap: [Object],
        source: [Object],
        sourcePath: [Object],
        legacyAST: [Object],
        ast: [Object],
        compiler: [Object],
        schema_version: [Function: schema_version],
        schemaVersion: [Function: schemaVersion],
        updated_at: [Function: updated_at],
        updatedAt: [Function: updatedAt] },
     _property_values: {},
     _json: 
      { contractName: 'HelloWorld',
        abi: [Object],
        bytecode: '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',
        deployedBytecode: '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',
        sourceMap: '25:172:0:-;;;;;;;;;;;;;;;;;',
        deployedSourceMap: '25:172:0:-;;;;;;;;;;;;;;;;;;;;;;;;;;;;;49:67;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;23:1:-1;8:100;33:3;30:1;27:2;8:100;;;99:1;94:3;90;84:5;80:1;75:3;71;64:6;52:2;49:1;45:3;40:15;;8:100;;;12:14;3:109;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;120:75:0;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;23:1:-1;8:100;33:3;30:1;27:2;8:100;;;99:1;94:3;90;84:5;80:1;75:3;71;64:6;52:2;49:1;45:3;40:15;;8:100;;;12:14;3:109;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;49:67:0;78:6;;:::i;:::-;92:19;;;;;;;;;;;;;;;;;;;;49:67;:::o;120:75::-;165:6;;:::i;:::-;186:4;179:11;;120:75;;;:::o;25:172::-;;;;;;;;;;;;;;;:::o',
        source: 'pragma solidity ^0.4.17;\ncontract HelloWorld {\n  function sayHello() returns (string) {\n    return "HelloWorld";\n  }\n\n  function echo(string name) constant returns (string) {\n    return name;\n  }\n}\n',
        sourcePath: '/Users/wangsanjun/Desktop/SmartContractDemo/HelloWorld/contracts/HelloWorld.sol',
        ast: [Object],
        legacyAST: [Object],
        compiler: [Object],
        networks: [Object],
        schemaVersion: '2.0.0',
        updatedAt: '2018-03-09T01:43:29.205Z' },
     setProvider: [Function: bound setProvider],
     new: [Function: bound new],
     at: [Function: bound at],
     deployed: [Function: bound deployed],
     defaults: [Function: bound defaults],
     hasNetwork: [Function: bound hasNetwork],
     isDeployed: [Function: bound isDeployed],
     detectNetwork: [Function: bound detectNetwork],
     setNetwork: [Function: bound setNetwork],
     resetAddress: [Function: bound resetAddress],
     link: [Function: bound link],
     clone: [Function: bound clone],
     addProp: [Function: bound addProp],
     toJSON: [Function: bound toJSON],
     web3: 
      Web3 {
        _requestManager: [Object],
        currentProvider: [Object],
        eth: [Object],
        db: [Object],
        shh: [Object],
        net: [Object],
        personal: [Object],
        bzz: [Object],
        settings: [Object],
        version: [Object],
        providers: [Object],
        _extend: [Object] },
     class_defaults: 
      { from: '0x4068364a85fa3bac7e83c45581397fe9c5111b39',
        gas: 6721975,
        gasPrice: 100000000000 },
     currentProvider: 
      HttpProvider {
        host: 'http://127.0.0.1:8545',
        timeout: 0,
        user: undefined,
        password: undefined,
        headers: undefined,
        send: [Function],
        sendAsync: [Function],
        _alreadyWrapped: true },
     network_id: '1520386125068' },
  abi: 
   [ { constant: false,
       inputs: [],
       name: 'sayHello',
       outputs: [Object],
       payable: false,
       stateMutability: 'nonpayable',
       type: 'function' },
     { constant: true,
       inputs: [Object],
       name: 'echo',
       outputs: [Object],
       payable: false,
       stateMutability: 'view',
       type: 'function' } ],
  contract: 
   Contract {
     _eth: 
      Eth {
        _requestManager: [Object],
        getBalance: [Object],
        getStorageAt: [Object],
        getCode: [Object],
        getBlock: [Object],
        getUncle: [Object],
        getCompilers: [Object],
        getBlockTransactionCount: [Object],
        getBlockUncleCount: [Object],
        getTransaction: [Object],
        getTransactionFromBlock: [Object],
        getTransactionReceipt: [Object],
        getTransactionCount: [Object],
        call: [Object],
        estimateGas: [Object],
        sendRawTransaction: [Object],
        signTransaction: [Object],
        sendTransaction: [Object],
        sign: [Object],
        compile: [Object],
        submitWork: [Object],
        getWork: [Object],
        coinbase: [Getter],
        getCoinbase: [Object],
        mining: [Getter],
        getMining: [Object],
        hashrate: [Getter],
        getHashrate: [Object],
        syncing: [Getter],
        getSyncing: [Object],
        gasPrice: [Getter],
        getGasPrice: [Object],
        accounts: [Getter],
        getAccounts: [Object],
        blockNumber: [Getter],
        getBlockNumber: [Object],
        protocolVersion: [Getter],
        getProtocolVersion: [Object],
        iban: [Object],
        sendIBANTransaction: [Function: bound transfer] },
     transactionHash: null,
     address: '0xb49e482f7b9201d5305e2d6a1bf1bad3d4c05540',
     abi: [ [Object], [Object] ],
     sayHello: 
      { [Function: bound ]
        request: [Function: bound ],
        call: [Function: bound ],
        sendTransaction: [Function: bound ],
        estimateGas: [Function: bound ],
        getData: [Function: bound ],
        '': [Circular] },
     echo: 
      { [Function: bound ]
        request: [Function: bound ],
        call: [Function: bound ],
        sendTransaction: [Function: bound ],
        estimateGas: [Function: bound ],
        getData: [Function: bound ],
        string: [Circular] },
     allEvents: [Function: bound ] },
  sayHello: 
   { [Function]
     call: [Function],
     sendTransaction: [Function],
     request: [Function: bound ],
     estimateGas: [Function] },
  echo: 
   { [Function]
     call: [Function],
     sendTransaction: [Function],
     request: [Function: bound ],
     estimateGas: [Function] },
  sendTransaction: [Function],
  send: [Function],
  allEvents: [Function: bound ],
  address: '0xb49e482f7b9201d5305e2d6a1bf1bad3d4c05540',
  transactionHash: null }
truffle(development)> contract.echo.call("HelloWorld")
'HelloWorld'
truffle(development)> contract.echo("HelloWorld")
'HelloWorld'

echo方法确实将我们输入的内容回传了。同时因为声明了 constant，我们不需要直接调用call()方法，truffle会自动选用call来呼叫。

另一点需要注意的，是这次如果还是用truffle migrate命令，我们会得到如下信息：

$ truffle migrate
Using network 'development'.
Network up to date.

Truffle会告诉你现在网络上的合约都已是最新的，但事实上刚刚程序中新增的方法并没有更新到内存块链上。要更新内存块链上已部署的程序，需要改写migrations中的脚本，但现在还不到介绍migration的时候。还好我们开发用的内存块链是怎么修改都没关系的ganache-cli，可以使用truffle migrate --reset命令直接重新在ganache-cli上部署一次。

总结

这篇文章非常简单，通过这篇文章，你将掌握如何配置开发环境、如何创建新项目、如何编译、如何部署合约以及了解整个智能合约开发的流程。

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