内容：
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
使用solidity语言撰写智能合约
Ethereum上的智能合约需要使用solidity语言来撰写。虽然还有其他能用来撰写智能合约的语言如Serpent（类Python）、lll（类Fortran），但目前看到所有公开的智能合约都是使用solidity撰写。
宣传上说，solidity是一种类似Javascript的语言，而且围绕着solidity的各种开发工具链，都是使用属于Javascript生态系的npm来提供的。但我觉得solidity还是比较像Java或C#。因为和Javascript不同，solidity与Java或C#同属于强类型（Strong Type，在定义变数时需要指定类型）语言、在定义函式（function）时同样需指定回传的类型（type）、同样也需要先编译才能执行。这些特性都是Javascript所不具备的。
开发前的准备
本文将使用当前最活跃的智能合约开发框架truffle为基础来开发。ENS（Ethereum Name Service）也是采用truffle框架。其他选择还有embark等。
就像一般网站或App开发一样，在提供公开服务之前，开发者会在自己用于写程序的电脑（又称作本机）或透过测试网络来测试程序执行的效果，测试完成后，才会部署到公开的网络上提供服务。开发区块链智能合约（程序）的过程也是如此。特别是公开链上所有写入或读取计算结果的操作都需要真金白银（虚拟代币），而且根据网络状况，每个公开链上的操作都需要要一小段反应时间（15秒~数分钟），这些等待颇浪费宝贵的开发时间。因此在开发的过程中，我们将使用testrpc工具在电脑上模拟智能合约所需的以太坊内存块链测试环境。
testrpc中也包含了Javascript版本的Ethereum虚拟机（Ethereum Virtual Machine），因此可以完整地执行智能合约。
此外，开发前还需准备一个合手的编辑器。我目前是使用Atom搭配solidity插件来开发。solidity插件除了支持语法高亮之外，也会透过Solium检查并提示基本的语法错误，相当方便。其他编辑器应该也有类似的插件可选择。
image
image
安装所需工具
首先开发机上必须装好Node.js，再使用以下命令安装所需的工具：
$ npm install -g ethereumjs-testrpc truffle
liyuechun:~ yuechunli$ npm install -g ethereumjs-testrpc truffle
/usr/local/bin/testrpc -> /usr/local/lib/node_modules/ethereumjs-testrpc/build/cli.node.js
/usr/local/bin/truffle -> /usr/local/lib/node_modules/truffle/build/cli.bundled.js
+ truffle@3.4.9
+ ethereumjs-testrpc@4.1.3
added 1 package and updated 7 packages in 76.132s
liyuechun:~ yuechunli$
启动Testrpc
安装好后随时可以使用testrpc命令来启动以太坊测试环境。
liyuechun:~ yuechunli$ testrpc
EthereumJS TestRPC v4.1.3 (ganache-core: 1.1.3)
Available Accounts
==================
(0) 0xbbd414b340f2255dab9d923428c97f0b65d9df81
(1) 0xe9869e3cf29b6fca81762c314df229c7c4fea25e
(2) 0xc79e72362a4511b9e499d186654332c4d6f569be
(3) 0x9a6f0651907c149d4173c03927144dbbba1473d4
(4) 0x5b13a5d6788752b26dd4e338aae2e01058ee145e
(5) 0xfc7f56d942ad5260be23ecee92a344aba1b7e7d8
(6) 0xc48dc22c6bacd6ade4421ab54f25bc45c1c51142
(7) 0x3fe2b7d4141dd0a456661f77086d055cbaf3b78f
(8) 0x567979fed26ca85e9d1b4ac919c840e3fc9857e2
(9) 0xb2eafe245f098eef1c2c1f466d9a8dcd58764c62
Private Keys
==================
(0) 947ab78e91133103612ca099d60e6c38cac5bb769f7f097c82d003cf058500bd
(1) 8ffe0ba8dc53e16944a17dddd3378b5fba0379cd84df4e5237b8b46d05b8762f
(2) ffe2e04e43e4106b247407656f5233bcc3e0c49730972d0df9c1d1093375e2ef
(3) a20e453dc44c76aaca6a22efdbb605c2ed9eea64c11317e683461e11bd105ea7
(4) 4748268ff1b828868dc56d07a1b121b427e1bdede5dbb3c14ef1254d9d26b1a5
(5) f9957e68c6d20d38b81604a0509e6c4591478bc754f87d5682564073705fbb46
(6) 34e648b23c0ace6b2b0893651d87f70be8496f97ecf6b7b4607b2acc4e05c9bd
(7) d2477cedec217e3fb19a5981dafbc125ef66ccc9dc7df29301d08a24da843cf5
(8) d319f85ccd80e55b2e707e05f09662632564c297248f8b96f82ea5eeaeef0851
(9) 88c33ac9f1062b82f9e82f86a0ce307e3bd8fcf683b9751232c2f193f5bdc668
HD Wallet
==================
Mnemonic: hire custom clinic expect fury fantasy try dress source spy viable flag
Base HD Path: m/44'/60'/0'/0/{account_index}
Listening on localhost:8545
可以看到testrpc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testrpc仅运行在內存中，因此每次重开时都会回到全新的状态。
一切准备就绪，我们可以开始建立第一份智能合约项目了。
建立项目
开启另一个终端窗口，输入以下命令以建立项目：
liyuechun:Desktop yuechunli$ mkdir SmartContractDemo
liyuechun:Desktop yuechunli$ cd SmartContractDemo/
liyuechun:SmartContractDemo yuechunli$ mkdir HelloWorld
liyuechun:SmartContractDemo yuechunli$ cd HelloWorld/
liyuechun:HelloWorld yuechunli$ truffle init
Downloading project...
Project initialized.
Documentation: http://truffleframework.com/docs
Commands:
Compile: truffle compile
Migrate: truffle migrate
Test: truffle test
liyuechun:HelloWorld yuechunli$ ls
contracts migrations test truffle.js
目录结构：
/contracts:存放智能合约原始代码的地方，可以看到里面已经有三个sol文件，我们开发的HelloWorld.sol文件就存放在这里。
/migrations:这是Truffle用来部署智能合约的功能，待会儿我们会修改2_deploy_contracts.js来部署HelloWorld.sol。
/test: 测试智能合约的代码放在这里，支持js与sol测试。 truffle.js: Truffle 的设置文档。
image.png
新建HelloWorld合约
在contracts文件夹下新建HelloWorld.sol文件，当然也可以直接在HelloWorld路径下面直接执行truffle create contract HelloWorld命令来创建HelloWorld.sol。
image
HelloWorld.sol文件內容如下：
pragma solidity ^0.4.4;
contract HelloWorld {
function sayHello() returns (string) {
return ("Hello World");
}
}
image
讲解
pragma solidity ^0.4.4;
第一行指名目前使用的solidity版本，不同版本的solidity可能会编译出不同的bytecode。^代表兼容solidity``0.4.4 ~ 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 ("Hello World");
}
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。
liyuechun:HelloWorld yuechunli$ ls
contracts migrations test truffle.js
liyuechun:HelloWorld yuechunli$ truffle compile
Compiling ./contracts/ConvertLib.sol...
Compiling ./contracts/HelloWorld.sol...
Compiling ./contracts/MetaCoin.sol...
Compiling ./contracts/Migrations.sol...
Writing artifacts to ./build/contracts
liyuechun:HelloWorld yuechunli$ ls
build contracts migrations test truffle.js
liyuechun:HelloWorld yuechunli$ cd build/
liyuechun:build yuechunli$ ls
contracts
liyuechun:build yuechunli$ cd contracts/
liyuechun:contracts yuechunli$ ls
ConvertLib.json HelloWorld.json MetaCoin.json Migrations.json
liyuechun:contracts yuechunli$ cat HelloWorld.json
{
"contract_name": "HelloWorld",
"abi": [
{
"inputs": [],
"payable": false,
"type": "constructor"
}
],
"unlinked_binary": "0x60606040523415600e57600080fd5b5b5b5b603680601e6000396000f30060606040525b600080fd00a165627a7a723058203ee98a767948e9bc08094df4a46ab0361f068b2a559032cf968df5bbf63e91430029",
"networks": {},
"schema_version": "0.0.5",
"updated_at": 1505805826302
}
liyuechun:contracts yuechunli$
image
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。打开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);
};
image
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：
liyuechun:HelloWorld yuechunli$ ls
build contracts migrations test truffle.js
liyuechun:HelloWorld yuechunli$ truffle migrate
Compiling ./contracts/HelloWorld.sol...
Writing artifacts to ./build/contracts
Using network 'development'.
Running migration: 1_initial_migration.js
Deploying Migrations...
... 0x218431f16a5cadc6347449808d981887c90b3872898af7cc9dc9b3280c07c184
Migrations: 0x64e9673cf962d21642a08635e6654fb7f2ea9bcd
Saving successful migration to network...
... 0xd9ec788c106df36b8491c95a0ab02ff1e5ef22c1965c910a2576e8259a00535c
Saving artifacts...
Running migration: 2_deploy_contracts.js
Deploying HelloWorld...
... 0x17774b4914d7bc7ab2505a53c59bda6a1fce30c9839d19d735290ca9140450ea
HelloWorld: 0x471a22ffe2bddd02e82853059871067e4c07a7f4
Saving successful migration to network...
... 0xe5e2e11cf5a63ca4517221c68dadb3cae2ca42cbfed93c09c575b6d5f275fc8b
Saving artifacts...
liyuechun:HelloWorld yuechunli$
如此一来合约已经部署到testrpc中。切换到testrpc窗口，可以看到testrpc有反应了。
image
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。
liyuechun:HelloWorld yuechunli$ ls
build contracts migrations test truffle.js
liyuechun:HelloWorld yuechunli$ truffle console
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],
abi: [Object],
network: [Function: network],
networks: [Function: networks],
address: [Object],
links: [Function: links],
events: [Function: events],
binary: [Function: binary],
unlinked_binary: [Object],
schema_version: [Function: schema_version],
updated_at: [Function: updated_at] },
_property_values: {},
_json:
{ contract_name: 'HelloWorld',
default_network: undefined,
abi: [Array],
unlinked_binary: '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',
networks: [Object],
schema_version: '0.0.5',
updated_at: 1505806918535 },
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: '0xbbd414b340f2255dab9d923428c97f0b65d9df81',
gas: 4712388,
gasPrice: 100000000000 },
currentProvider:
HttpProvider {
host: 'http://localhost:8545',
timeout: 0,
send: [Function],
sendAsync: [Function],
_alreadyWrapped: true },
network_id: '1505794143155' },
abi:
[ { constant: false,
inputs: [],
name: 'sayHello',
outputs: [Array],
payable: false,
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: '0x471a22ffe2bddd02e82853059871067e4c07a7f4',
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: '0x471a22ffe2bddd02e82853059871067e4c07a7f4',
transactionHash: null }
truffle(development)> contract.sayHello.call()
'Hello World'
truffle(development)>
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'
这里直接呼叫contract.sayHello()也会得到一样的结果。truffle-contract提供使用call()来读取只读（read only）的数据，这样就不需提供gas。因此如果遇到的操作需要向区块链写入数据，我们就不能用call语句了。
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testrpc上，再透过truffle console执行看看结果。
liyuechun:HelloWorld yuechunli$ ls
build contracts migrations test truffle.js
liyuechun:HelloWorld yuechunli$ truffle compile
Compiling ./contracts/HelloWorld.sol...
Writing artifacts to ./build/contracts
liyuechun:HelloWorld yuechunli$ truffle migrate --reset
Using network 'development'.
Running migration: 1_initial_migration.js
Replacing Migrations...
... 0x64cdc42e08a7e3f8070c46d4877ba246d95cbbccbfe1b9abd2450cfc02b48eda
Migrations: 0x42843f6a470b84e2669f19686a223c1bdefb6f4d
Saving successful migration to network...
... 0x57042b767c0f40a4f88ce855e39549010d6d5ae5f880771a45c1f7f36ea0e5b3
Saving artifacts...
Running migration: 2_deploy_contracts.js
Replacing HelloWorld...
... 0x2330e3264aae9d6be3744d8fc71d235fc6dc2934d33ff5159ae209df4cf8f12b
HelloWorld: 0xbf68789cdd6be1577339e8c739abfa1190c31b6c
Saving successful migration to network...
... 0xb4b706d7004654215067ea5954a32f0562b32724d1c646dc43b688b466b10159
Saving artifacts...
liyuechun:HelloWorld yuechunli$ truffle console
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],
abi: [Object],
network: [Function: network],
networks: [Function: networks],
address: [Object],
links: [Function: links],
events: [Function: events],
binary: [Function: binary],
unlinked_binary: [Object],
schema_version: [Function: schema_version],
updated_at: [Function: updated_at] },
_property_values: {},
_json:
{ contract_name: 'HelloWorld',
default_network: undefined,
abi: [Array],
unlinked_binary: '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',
networks: [Object],
schema_version: '0.0.5',
updated_at: 1505809278810 },
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: '0xbbd414b340f2255dab9d923428c97f0b65d9df81',
gas: 4712388,
gasPrice: 100000000000 },
currentProvider:
HttpProvider {
host: 'http://localhost:8545',
timeout: 0,
send: [Function],
sendAsync: [Function],
_alreadyWrapped: true },
network_id: '1505794143155' },
abi:
[ { constant: false,
inputs: [],
name: 'sayHello',
outputs: [Array],
payable: false,
type: 'function' },
{ constant: true,
inputs: [Array],
name: 'echo',
outputs: [Array],
payable: false,
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: '0xbf68789cdd6be1577339e8c739abfa1190c31b6c',
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: '0xbf68789cdd6be1577339e8c739abfa1190c31b6c',
transactionHash: null }
truffle(development)> contract.echo("春哥微信:liyc1215")
'春哥微信:liyc1215'
truffle(development)>
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testrpc，可以使用truffle migrate --reset命令直接重新在testrpc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。
参考资料
[1] Solidity http://solidity.readthedocs.io/en/latest/index.html
[2] Solidity線上編輯器 https://ethereum.github.io/browser-solidity/
[3] Truffle Framework http://truffleframework.com/
[4] Embark Framework https://github.com/iurimatias/embark-framework
[5] ENS也使用Truffle框架 https://github.com/ethereum/ens
[6] https://github.com/ethereumjs/testrpc
[7] https://github.com/ethereumjs/ethereumjs-vm
[8] HelloWorld範例修改自 https://app.pluralsight.com/library/courses/blockchain-fundamentals/
[9] Truffle issue on windows http://truffleframework.com/docs/advanced/configuration#resolving-naming-conflicts-on-windows
[10] https://medium.com/taipei-ethereum-meetup/ethereum-dapp-tutorial-push-button-cae3810086a4
[11] Solidity支援的型別(Type) https://solidity.readthedocs.io/en/develop/types.html
[12] Solium syntax check https://github.com/duaraghav8/Solium
[13] https://medium.com/taipei-ethereum-meetup/如何撰寫智能合約-smart-contract-i-363d06b1965b
[14] http://truffleframework.com/docs/getting_started/contracts
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