Upgradeable smart contracts are a desirable design practice given today’s extremely important and ever-changing landscape for smart contract security. In this article, we deploy a plain ERC20 contract, and later upgrade it to a mintable token contract to allow for the functionality of minting new tokens. However, it is important to keep in mind that there are some key design principles to be followed while coding such contracts. On the surface, smart contract upgradeability may seem like a pretty cool feature to have. However, it violates a fundamental property of Blockchains — . I will be creating a follow-up article which addresses this topic. But for now, let’s focus on the implementation alone. immutability We use to achieve our task. ZeppelinOS Refer to the diagram below for a simple reference on how ZeppelinOS achieves upgradeability. I’m not going to delve deeper into the technical aspects as they already have pretty good in place. documentation Let’s get into writing code. For this deployment, I’m going to use as my local Ethereum node. I’m also going to assume you already have node.js installed on your system. Ganache Install ZeppelinOS using the command below npm install --global zos If you are on Windows, and you’re running into issues with check out this . node-gyp, guide 2. Let’s say we’re creating the project Create a folder and initialize the project. demo-token. mkdir demo-token && cd demo-token npm init zos init demo-token This will create a file along with a . truffle-config.js zos.json Install the ZeppelinOS libraries and link the standard libraries with the following commands npm install zos-lib zos link openzeppelin-zos 3. Now let’s write that upgradeable smart contract. In the folder create a new file with the contents provided below contracts, DemoToken.sol pragma solidity ^0.4.21;import "zos-lib/contracts/migrations/Migratable.sol";import "openzeppelin-zos/contracts/token/ERC20/DetailedERC20.sol";import "openzeppelin-zos/contracts/token/ERC20/StandardToken.sol";import "openzeppelin-zos/contracts/ownership/Ownable.sol"; contract DemoToken is Migratable, StandardToken, DetailedERC20, Ownable  {function initialize(uint256 initialSupply, address InitialAccount, string _name, string _symbol, uint8 _decimals) isInitializer("DemoToken", "0.1") public{totalSupply_ = initialSupply;balances[InitialAccount] = initialSupply;DetailedERC20.initialize(_name, _symbol, _decimals);Ownable.initialize(InitialAccount);}} Note that in ZeppelinOS, your smart contract should not specify a constructor. Initialization for the parameters can be defined inside function. The modifier accepts the name you wish to give for this version of your contract along with the version number. initialize() isInitializer() 4. Now let’s add the token into ZeppelinOS zos add DemoToken If all goes well, you should get the above output 5. Time to deploy. Setup your correctly to point to your local ganache node and execute the command below truffle-config.js zos push --deploy-stdlib --network local Note: In the above command we are also deploying the Zeppelin standard libraries in your local ganache instance. This need not be done when deploying to any of the test networks or the mainnet. Note: In my experience Ganache runs on port 7545 by default. You might have to change your file accordingly. You can refer to my file below truffle-config.js truffle-config.js 'use strict'; module.exports = {networks: {local: {host: 'localhost',port: 7545,gas: 5000000,network_id: '*'}}}; If correctly done, you should get the below output 6. Now we have to initialize the smart contract with the parameters provided in the method. DemoToken initialize zos create DemoToken --init initialize --args 100,"<Your Ganache Address>","Demo","DMO",18 --network local The above command creates 100 at the specified Ganache account. Success would look like this DemoTokens 7. Let’s try out our newly created tokens. Open a new truffle window with the command below npx truffle console --network local truffle(local)> demo = DemoToken.at("<ContractAddress>") Enter the proxy address as the contract address. It is the last line in the above screenshot. In my case, it was If successful the object should appear in full. 0x0caac69787f1db70308d4fdd1c416d6cf23284b5. demo 8. Try out two simple transactions to see if everything works well truffle(local)> demo.balanceOf(web3.eth.accounts[0])>BigNumber { s: 1, e: 2, c: [ 100 ] } truffle(local)> demo.transfer(web3.eth.accounts[1],20) truffle(local)> demo.balanceOf(web3.eth.accounts[0])>BigNumber { s: 1, e: 1, c: [ 80 ] } That’s about it. You’ve just created your very first upgradeable smart contract! 9. Time for the upgrade. Let’s revisit , and make it a Mintable ERC20 contract. DemoToken.sol pragma solidity ^0.4.21;import "zos-lib/contracts/migrations/Migratable.sol";import "openzeppelin-zos/contracts/token/ERC20/DetailedERC20.sol";import "openzeppelin-zos/contracts/token/ERC20/StandardToken.sol";import "openzeppelin-zos/contracts/ownership/Ownable.sol"; contract DemoToken is Migratable, StandardToken, DetailedERC20, Ownable  {function initialize(uint256 initialSupply, address InitialAccount, string _name, string _symbol, uint8 _decimals) isInitializer("DemoToken", "0") public{totalSupply_ = initialSupply;balances[InitialAccount] = initialSupply;DetailedERC20.initialize(_name, _symbol, _decimals);Ownable.initialize(InitialAccount);} event Mint(address indexed to, uint256 amount);event MintFinished(); bool public mintingFinished = false; modifier canMint() {require(!mintingFinished);_;} function mint(address _to, uint256 _amount) onlyOwner canMint public returns (bool) {totalSupply_ = totalSupply_.add(_amount);balances[_to] = balances[_to].add(_amount);emit Mint(_to, _amount);emit Transfer(address(0), _to, _amount);return true;} function finishMinting() onlyOwner canMint public returns (bool) {mintingFinished = true;emit MintFinished();return true;} } 10. Exit the truffle console and repeat the command in step 5 zos push --network local Note: There is no need to redeploy stdlib files again in your local ethereum node. Note: In the file, see how the object under the “ key updated to your new DemoToken contract address, but the key under “proxies” still points to your old contract address. We fix this in the next step. zos.local.json contracts” 11. Update ZeppelinOS with the new contract zos update DemoToken --network local 12. Now let’s check out the upgraded features. On a new command window, try out the following npx truffle console --network local truffle(local)> demo = DemoToken.at("<your-proxy-address>") In my case, it’s again going to be 0x0caac69787f1db70308d4fdd1c416d6cf23284b5 truffle(local)> demo.balanceOf(web3.eth.accounts[0])>BigNumber { s: 1, e: 1, c: [ 80 ] }truffle(local)> demo.mintingFinished()>falsetruffle(local)> demo.mint(web3.eth.accounts[0],100)truffle(local)> demo.balanceOf(web3.eth.accounts[0])>BigNumber { s: 1, e: 2, c: [ 180 ] } Pretty cool eh? Created a plain ERC20 contract. Later upgraded it to a Mintable contract. Then minted a few tokens to myself. As unethical as it can get! If you have queries regarding the above or you happen to be in the market for a Blockchain expert for your project, book me for free, for a quick 30-minute online consulting session. I have a new initiative called which will facilitate this. Consult Me Live Cheers.

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Upgradeable Smart Contracts Made Easy

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