Solidity in 5 Minutes

Cae2dd246ed83dd458e4ce5f927aa2f7?s=47 U-Zyn Chua
November 26, 2016

Solidity in 5 Minutes

Creating Decentralized Apps on Ethereum Blockchain

Presented at JSConf.Asia 2016

Code snippets: https://bit.ly/SGDT-sol

Cae2dd246ed83dd458e4ce5f927aa2f7?s=128

U-Zyn Chua

November 26, 2016
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  1. 2.

    @uzyn Smart contracts are computer protocols that facilitate, verify, or

    enforce the negotiation or performance of a contract, or that make a contractual clause unnecessary. @uzyn
  2. 3.

    @uzyn Smart contracts are computer protocols that facilitate, verify, or

    enforce the negotiation or performance of a contract, or that make a contractual clause unnecessary.
  3. 13.

    @uzyn are stored permanently on EVM. Data types Boolean bool

    Integer int / uint (unsigned) Ethereum address address Bytes and String bytes / string State variables
  4. 14.

    @uzyn mapping (address => uint) likes; function like(address _friend) public

    { likes[_friend]++; } Functions and Modifiers modifier onlyOwner { if (msg.sender != owner) throw; _; } function makeAdmin(_candidate) public onlyOwner { admin = _candidate; } The rest of the function goes here Looks pretty much like a JS function.
  5. 15.

    @uzyn Function Visibilities 1.public a. Visible externally and interally b.

    Automatically creates accessor. 2.private a. Only visible in current contract Remember, on blockchain, all data is publicly viewable! also internal and external.
  6. 16.

    @uzyn Arrays, Mappings & Structs // mapping - non-iterable (recommended)

    mapping (address => uint) likes; // array - iterable address[] public friends; // struct struct Person { string name; address wallet; uint lastSeen; } Hash Table
  7. 22.

    @uzyn Roles 1. Issuer a. Able to issue SGDT, after

    putting up equivalent SGD collateral. b. SGDT <==> SGD exchanger & guarantor. 2. User a. Able to freely transact SGDT. 3.Authority a. Grant license to issuers. http://bit.ly/SGDT-sol
  8. 23.

    @uzyn pragma solidity ^0.4.2; contract SGDT { /* Public variables

    of the token */ uint8 public decimals = 2; uint public totalSupply = 0; address public authority; /* This creates an array with all balances */ mapping (address => uint) public balanceOf; mapping (address => uint) public issuedBy; mapping (address => bool) public isIssuer; } Define state variables http://bit.ly/SGDT-sol
  9. 24.

    @uzyn Modifiers modifier onlyIssuer { if (isIssuer[msg.sender] != true) {

    throw; } _; } modifier onlyAuthority { if (msg.sender != authority) { throw; } _; } http://bit.ly/SGDT-sol
  10. 25.

    @uzyn Events event Transfer(address from, address to, uint value); event

    TokenIssued(address by); http://bit.ly/SGDT-sol Notify your JS daemon 
 on contract updates
  11. 26.

    @uzyn Issuer functions function issue(uint _value) public onlyIssuer { issuedBy[msg.sender]

    += _value; balanceOf[msg.sender] += _value; TokenIssued(msg.sender, _value); // Event } Can you work on the redeem() function? http://bit.ly/SGDT-sol
  12. 27.

    @uzyn User functions // Transfer SGDT function transfer(address _to, uint

    _value) public { if (balanceOf[msg.sender] < _value) { throw; // Check if the sender has enough } balanceOf[msg.sender] -= _value; // Subtract from the sender balanceOf[_to] += _value; // Add the same to the recipient // Notify anyone listening that this transfer took place Transfer(msg.sender, _to, _value); } http://bit.ly/SGDT-sol
  13. 28.

    @uzyn Authority functions function addIssuer(address _newIssuer) public onlyAuthority { isIssuer[_newIssuer]

    = true; } Can you add removeIssuer() function? http://bit.ly/SGDT-sol
  14. 29.

    @uzyn web3.js Ethereum JavaScript API Because Web 2.0 is so

    year 2000. Allows interaction with JS 
 (Node.JS and browser)