Hi,
I tested implementing this contract, with the openzeppelin-solidity 2.5 includes and it worked very well
Later, testing other things, I updated the includes openzeppelin-solidity 3X and my previous code did not work
I'm trying to adjust the code so that, taking advantage of the openzeppelin-solidity 3.x libraries, it works, but I'm not moving from here:
contract MyToken is ERC20 {
uint256 private _minimumSupply = 2000 * (10 ** 18);
/**
* @dev Constructor that gives msg.sender all of existing tokens.
*/
constructor () public ERC20( "MyToken", "MTN") {
_mint(msg.sender, 10000 * (10 ** uint256(decimals())));
}
function transfer(address to, uint256 amount) public returns (bool) {
return super.transfer(to, _partialBurn(amount));
}
function transferFrom(address from, address to, uint256 amount) public returns (bool) {
return super.transferFrom(from, to, _partialBurn(amount));
}
function _partialBurn(uint256 amount) internal returns (uint256) {
uint256 burnAmount = _calculateBurnAmount(amount);
if (burnAmount > 0) {
_burn(msg.sender, burnAmount);
}
return amount.sub(burnAmount);
}
function _calculateBurnAmount(uint256 amount) internal view returns (uint256) {
uint256 burnAmount = 0;
// burn amount calculations
if (totalSupply() > _minimumSupply) {
burnAmount = amount.div(100);
uint256 availableBurn = totalSupply().sub(_minimumSupply);
if (burnAmount > availableBurn) {
burnAmount = availableBurn;
}
}
return burnAmount;
}
}
I am testing in remix, and I try to include the files corresponding to version 2.5 again, they do not work,
I understand that they were overwritten and only the includes from version 3.x are kept
Can you explain to me what the difference is and how to correct it
Thank you very much
1 Like
Hi @Refresko,
If you create a fee on transfer or deflationary token (burn a percentage on transfer) this can cause issues when used with other contracts such as: https://medium.com/balancer-protocol/incident-with-non-standard-erc20-deflationary-tokens-95a0f6d46dea
From: Points to consider when creating a fungible token (ERC20, ERC777)
You were missing the keyword override that was introduced in Solidity 0.6, see: https://docs.soliditylang.org/en/v0.7.5/060-breaking-changes.html?highlight=override#how-to-update-your-code
The following code has not been tested nor audited. Deflationary tokens can cause issues. (see above)
// SPDX-License-Identifier: MIT
pragma solidity ^0.6.2;
import "https://github.com/OpenZeppelin/openzeppelin-contracts/blob/v3.1.0/contracts/token/ERC20/ERC20.sol";
contract MyToken is ERC20 {
uint256 private _minimumSupply = 2000 * (10 ** 18);
/**
* @dev Constructor that gives msg.sender all of existing tokens.
*/
constructor () public ERC20( "MyToken", "MTN") {
_mint(msg.sender, 10000 * (10 ** uint256(decimals())));
}
function transfer(address to, uint256 amount) public override returns (bool) {
return super.transfer(to, _partialBurn(amount));
}
function transferFrom(address from, address to, uint256 amount) public override returns (bool) {
return super.transferFrom(from, to, _partialBurn(amount));
}
function _partialBurn(uint256 amount) internal returns (uint256) {
uint256 burnAmount = _calculateBurnAmount(amount);
if (burnAmount > 0) {
_burn(msg.sender, burnAmount);
}
return amount.sub(burnAmount);
}
function _calculateBurnAmount(uint256 amount) internal view returns (uint256) {
uint256 burnAmount = 0;
// burn amount calculations
if (totalSupply() > _minimumSupply) {
burnAmount = amount.div(100);
uint256 availableBurn = totalSupply().sub(_minimumSupply);
if (burnAmount > availableBurn) {
burnAmount = availableBurn;
}
}
return burnAmount;
}
}
Friend, thanks for the reply.
And thanks for the warning of the “risk” deflationary tokens and for correcting and demonstrate the absence of the word override
Regards!!!
1 Like
Sorry that such simple things make me ask you, but I do not understand the error
I am trying to test in VS code studio
I already have the WLS 2 and am using Truffle
So, in that way, I’m testing the same thing:
// SPDX-License-Identifier: MIT
pragma solidity ^0.7.0;
import "@openzeppelin/contracts/token/ERC20/ERC20.sol";
import "@openzeppelin/contracts/token/ERC20/ERC20Burnable.sol";
/**
* @title MyToken
* @dev 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 MyToken is ERC20 {
uint256 private _minimumSupply = 2000 * (10 ** 18);
/**
* @dev Constructor that gives msg.sender all of existing tokens.
*/
constructor () public ERC20( "Mauus", "MGU") {
_mint(msg.sender, 2000000 * (10 ** uint256(decimals())));
}
function transfer(address to, uint256 amount) public override returns (bool) {
return super.transfer(to, _partialBurn(amount));
}
function transferFrom(address from, address to, uint256 amount) public override returns (bool) {
return super.transferFrom(from, to, _partialBurn(amount));
}
function _partialBurn(uint256 amount) internal returns (uint256) {
uint256 burnAmount = _calculateBurnAmount(amount);
if (burnAmount > 0) {
_burn(msg.sender, burnAmount);
}
uint256 sss = amount.sub(burnAmount);
return 545;
}
function _calculateBurnAmount(uint256 amount) internal view returns (uint256) {
uint256 burnAmount = 0;
// burn amount calculations
if (totalSupply() > _minimumSupply) {
burnAmount = amount.div(100);
uint256 availableBurn = totalSupply().sub(_minimumSupply);
if (burnAmount > availableBurn) {
burnAmount = availableBurn;
}
}
return burnAmount;
}
}
and I get this error
“Member” sub “not found or not visible after argument-dependent lookup in uint256.” and I don’t understand why
can you help me
in truffle-config.js i am using :
solc: {
version: "0.7.5", // Fetch exact version from solc-bin (default: truffle's version)
// docker: true, // Use "0.5.1" you've installed locally with docker (default: false)
// settings: { // See the solidity docs for advice about optimization and evmVersion
// optimizer: {
// enabled: false,
// runs: 200
// },
// evmVersion: "byzantium"
// }
}
1 Like
Hi @Refresko,
You have changed to Solidity 0.7 so you need to add using SafeMath for uint256; to your contract.
_From: https://docs.soliditylang.org/en/v0.7.5/070-breaking-changes.html#functions-and-events_
using A for B only affects the contract it is mentioned in. Previously, the effect was inherited. Now, you have to repeat the using statement in all derived contracts that make use of the feature.
1 Like
friend, thank you very much for your reply
with it, remove that error message about the sub,
--------------Edited, retesting before asking
1 Like
how do i get back the tokens i burned