How do I include a burn function to this ERC20 token Solidity code?

Support Contracts
3

Hi @cryptcode,

You may want to change to use the OpenZeppelin Contracts ERC20 implementation for your ERC20 token as so far your token is straight forward.

SimpleToken.sol

The following is a simple ERC20 token.

pragma solidity ^0.5.0;

import "@openzeppelin/contracts/token/ERC20/ERC20.sol";
import "@openzeppelin/contracts/token/ERC20/ERC20Detailed.sol";

/**
 * @title SimpleToken
 * @dev Very simple ERC20 Token example, where all tokens are pre-assigned to the creator.
 * Note they can later distribute these tokens as they wish using `transfer` and other
 * `ERC20` functions.
 */
contract SimpleToken is ERC20, ERC20Detailed {

    /**
     * @dev Constructor that gives msg.sender all of existing tokens.
     */
    constructor () public ERC20Detailed("SimpleToken", "SIM", 18) {
        _mint(msg.sender, 10000 * (10 ** uint256(decimals())));
    }
}

SimpleBurnableToken.sol

To change to make SimpleToken burnable, we can just inherit from ERC20Burnable

pragma solidity ^0.5.0;

import "@openzeppelin/contracts/token/ERC20/ERC20.sol";
import "@openzeppelin/contracts/token/ERC20/ERC20Detailed.sol";
import "@openzeppelin/contracts/token/ERC20/ERC20Burnable.sol";

/**
 * @title SimpleBurnableToken
 * @dev Very simple ERC20 Token example, where all tokens are pre-assigned to the creator.
 * Note they can later distribute these tokens as they wish using `transfer` and other
 * `ERC20` functions.
 */
contract SimpleBurnableToken is ERC20, ERC20Detailed, ERC20Burnable {

    /**
     * @dev Constructor that gives msg.sender all of existing tokens.
     */
    constructor () public ERC20Detailed("SimpleToken", "SIM", 18) {
        _mint(msg.sender, 10000 * (10 ** uint256(decimals())));
    }
}

Deploy

We can deploy the token using OpenZeppelin CLI 2.8: Release Candidate (npm i @openzeppelin/cli@rc) and deploy as a regular contract (to make it upgradeable we would need to inherit from @openzeppelin/contracts-ethereum-package)

$ npx oz deploy
✓ Compiled contracts with solc 0.5.16 (commit.9c3226ce)
? Choose the kind of deployment regular
? Pick a network development
? Pick a contract to deploy SimpleBurnableToken
✓ Deployed instance of SimpleBurnableToken
0xe78A0F7E598Cc8b0Bb87894B0F60dD2a88d6a8Ab

Check total supply

$ npx oz call
? Pick a network development
? Pick an instance SimpleBurnableToken at 0xe78A0F7E598Cc8b0Bb87894B0F60dD2a88d6a8Ab
? Select which function totalSupply()
✓ Method 'totalSupply()' returned: 10000000000000000000000
10000000000000000000000

Burn

Burn from the current account.

$ npx oz send-tx
? Pick a network development
? Pick an instance SimpleBurnableToken at 0xe78A0F7E598Cc8b0Bb87894B0F60dD2a88d6a8Ab
? Select which function burn(amount: uint256)
? amount: uint256: 10000000000000000000

----

Let me know if you have any questions.
✓ Transaction successful. Transaction hash: 0xd9a85bc729a747aae0a164e9dda9c98eb40141003056505e8c6e7b51c5dd1838
Events emitted:
 - Transfer(0x90F8bf6A479f320ead074411a4B0e7944Ea8c9C1, 0x0000000000000000000000000000000000000000, 10000000000000000000)

Check total supply (after burning)

$ npx oz call
? Pick a network development
? Pick an instance SimpleBurnableToken at 0xe78A0F7E598Cc8b0Bb87894B0F60dD2a88d6a8Ab
? Select which function totalSupply()
✓ Method 'totalSupply()' returned: 9990000000000000000000
9990000000000000000000
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