OpenZeppelinNotes.md

OpenZeppelin

• Public
• Opensource
• Introduce standards
• Same structure, libraries, and contracts

Access Control

This tidbit is particularly interesting https://docs.openzeppelin.com/contracts/4.x/access-control

How-to

1. Create a new project with npm init and truffle init commands
2. Add contracts to project with npm install @openzeppelin/contracts
3. You should now have node_modules directory under your token project
4. Import the openzeppelin contracts you want to use
5. run truffle develop, compile, migrate *migrate --reset if you've run it before already
6. let instance = await Token.deployed()
7. Interact via console e.g instance.symbol(), instance.balanceOf(accounts[0])

BN: 3e8

BN = Big Number

How to conver it to something human readable

let result = await instance.balanceOf(accounts[0])
result.toNumber()
result.toString() 

Particularly powerful utility: Reentrancy Guard

Prevent a function from being entered again if it's already running by the same process.

modifier nonReentrant() { 
    require(_status != _ENTERED, "ReentrancyGuard: reentrant call"); 
    _status = _ENTERED; 
    _; 
    _status = _NOT_ENTERED; 
}

then you can just use that function like a modifier after importing it.

isContract()

Make sure the address is a contract or a wallet

7 OpenZeppelin Contracts You Should Always Use

Full list here

1. Ownable
2. Roles
3. SafeMath
4. SafeCast
5. ERC20Detailed
6. ERC721Enumerable & ERC721Full

pragma solidity ^0.5.0;

import "@openzeppelin/contracts/token/ERC721/ERC721Full.sol";
import "@openzeppelin/contracts/drafts/Counters.sol";

contract GameItem is ERC721Full {
    using Counters for Counters.Counter;
    Counters.Counter private _tokenIds;

    constructor() ERC721Full("GameItem", "ITM") public {
    }

    function awardItem(address player, string memory tokenURI) public returns (uint256) {
        _tokenIds.increment();

        uint256 newItemId = _tokenIds.current();
        _mint(player, newItemId);
        _setTokenURI(newItemId, tokenURI);

        return newItemId;
    }
}

7. Address (check if contract)