Smart Contract & Solidity Solidity

winterj.me@gmail.com

JungWinter

Smart Contract

Smart Contract

•

• 1994 Nick Szabo

•

•

Transaction

Smart Contract

•

•

•

•

• Contacting external services, Enforcing on-chain payments

• (= )

Ethereum Contract

Bitcoin Contract

• Script

• OPCODE

• Output Input Public Key  HASH  CHECKSIG  Private Key TRUE

Ethereum Contract

•  Turing Complete

• APPLY(S)=S’ (APPLY: , S: , S’: )

• Smart Contract

• Loop , Contract Account, Block Transaction , Gas

Loop Gas

• Operation Gas Cost

• Transaction fee = Gas_used * Gas_price[Gwei]1 Gwei = 0.000000001 ETH

• Gas = Gas

Smart Contract Code• Smart Contract

Smart Contract Code

• EVM(Ethereum Virtual Machine) EVM

• • Mutan: C Deprecated• LLL: Low level OPCODE• Serpent: Python • Solidity: Javascript

Smart Contract

(https://maniara.github.io/sc_lecture.pdf)

Solidity

Solidity Hello Worldpragma solidity ^0.4.0;

contract SimpleStorage { uint storedData;

function set(uint x) { storedData = x; }

function get() constant returns (uint retVal) { return storedData; }}

pragma

constant

returns

uint

http://solidity.readthedocs.io/en/develop/introduction-to-smart-contracts.html

Solidity Hello Worldpragma solidity ^0.4.0;

contract SimpleStorage { uint storedData;

function set(uint x) { storedData = x; }

function get() constant returns (uint retVal) { return storedData; }}

pragma

constant

returns

uint

^0.4.0 Solidity 0.5.0 npm

^1.2.3 → >=1.2.3 <2.0.0 ^0.2.3 → >=0.2.3 <0.3.0 ^0.0.3 → >=0.0.3 <0.0.4

Solidity Hello Worldpragma solidity ^0.4.0;

contract SimpleStorage { uint storedData;

function set(uint x) { storedData = x; }

function get() constant returns (uint retVal) { return storedData; }}

pragma

constant

returns

uint

constant

State constant Gas

Modifier

. 0.4.16 constant view pure constant view alias pure pure

Solidity Hello Worldpragma solidity ^0.4.0;

contract SimpleStorage { uint storedData;

function set(uint x) { storedData = x; }

function get() constant returns (uint retVal) { return storedData; }}

pragma

constant

returns

uint

return

1

Solidity Hello Worldpragma solidity ^0.4.0;

contract SimpleStorage { uint storedData;

function set(uint x) { storedData = x; }

function get() constant returns (uint retVal) { return storedData; }}

pragma

constant

returns

uint

uint unsigned int uint8 uint256 uint uint256

Solidity Code → Byte Code

SMART CONTRACT (http://goodjoon.tistory.com/261)

SMART CONTRACT (http://goodjoon.tistory.com/261)

dApp

Contract Meta data

pragma solidity ^0.4.0;

contract Coin{ address public minter; mapping (address => uint ) public balances;

event Sent (address from, address to, uint amount);

function Coin() { minter = msg.sender; } function mint(address receiver, uint amount) { if (msg.sender != minter) return; balances[receiver] += amount; }

function send(address receiver, uint amount) { if (balances[msg.sender] < amount) return; balances[msg.sender] -= amount; balances[receiver] += amount; Sent(msg.sender, receiver, amount); }

}

http://solidity.readthedocs.io/en/develop/introduction-to-smart-contracts.html

address

public

mapping

event

msg

address

public

mapping

event

msg

http://solidity.readthedocs.io/en/develop/introduction-to-smart-contracts.html

20byte( ) balance( ), transfer( )

Python dict . mapping(address => uint) address key uint value dict

public address public minter; function minter() returns (address) { return minter; }

), msg.sender , msg.value Wei(Ether)

.data, .gas, .sig

. listener

(3)—   (https://medium.com/@soonhyungjung/ - - -3- - - -44a9d58d687a)

pragma solidity^0.4.0;

contract Bank { uint totalDeposit; mapping(address=> uint) balanceOf; function deposit() payable { balanceOf[msg.sender] += msg.value; totalDeposit += msg.value; } function withdraw(uint _amount) payable { balanceOf[msg.sender] -= _amount; totalDeposit -= _amount; msg.sender.call.value(_amount)(); // msg.sender.transfer(_amount); } function getTotalBalance() constant returns(uint) { return totalDeposit; } function getBalance(address _account) constant returns(uint) { return balanceOf[_account]; }}

payable

payable & modifierpragma solidity ^0.4.11;

contract Purchase { address public seller;

modifier onlySeller() { // Modifier require(msg.sender == seller); _; }

function abort() onlySeller { // Modifier usage // ... }}

Solidity modifier  payable (https://medium.com/@ggogun/solidity -modifier- -payable-d892a833920c)

Python Decorator, Ruby on Rails before_filter _; modifier .

TODO

• Solidity Voting

• Campaign & Crowdfunding

• Custom Token

• Why Many Smart Contract Use Cases Are Simply Impossible (https://

www.coindesk.com/three-smart-contract-misconceptions/)

• Calculating Costs in Ethereum Contracts (https://hackernoon.com/ether-purchase-power-df40a38c5a2f)

• Gas Cost from Yellow Paper (http://bit.ly/2xfBHWN)

• SMART CONTRACT - (http://goodjoon.tistory.com/253)

• SMART CONTRACT (http://goodjoon.tistory.com/261)

• dApp (http://www.chaintalk.io/archive/lecture/86)

• Solidity (https://www.gitbook.com/book/ggs134/solidityguide)

• Solidity (https://solidity.readthedocs.io/en/develop/)