How do I integrated a cap into a templated contract from the wizard

Support Contracts
1

I created a token contract using the OpenZepplin Wizard and would like to introduce a cap using this abstract contract.

import "@openzeppelin/contracts/token/ERC20/extensions/ERC20Capped.sol";

The full contract is below. When I deploy, I'm able to mint as many tokens as I want. I would greatly appreciate any tips or links to examples, suggestions.

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.9;

import "@openzeppelin/contracts/token/ERC20/ERC20.sol";
import "@openzeppelin/contracts/token/ERC20/extensions/ERC20Burnable.sol";
import "@openzeppelin/contracts/security/Pausable.sol";
import "@openzeppelin/contracts/access/Ownable.sol";
import "@openzeppelin/contracts/token/ERC20/extensions/draft-ERC20Permit.sol";

// How do I integrated this:
import "@openzeppelin/contracts/token/ERC20/extensions/ERC20Capped.sol";

/// @custom:security-contact me@example.com
contract MyTokenC is ERC20, ERC20Burnable, Pausable, Ownable, ERC20Permit {
    constructor() ERC20("MyToken-C", "MTKC") ERC20Permit("MyToken-C") {}

    function pause() public onlyOwner {
        _pause();
    }

    function unpause() public onlyOwner {
        _unpause();
    }

    function mint(address to, uint256 amount) public onlyOwner {
        _mint(to, amount);
    }

    function _beforeTokenTransfer(address from, address to, uint256 amount)
        internal
        whenNotPaused
        override
    {
        super._beforeTokenTransfer(from, to, amount);
    }
}

:computer: Environment

Polygon
Remix
OpenZepplin Wizard

2

I believe I figured it out, but any comments suggestions would be appreciated. The current draft is:

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.9;

import "@openzeppelin/contracts/token/ERC20/extensions/ERC20Capped.sol";
import "@openzeppelin/contracts/token/ERC20/ERC20.sol";
import "@openzeppelin/contracts/token/ERC20/extensions/ERC20Burnable.sol";
import "@openzeppelin/contracts/security/Pausable.sol";
import "@openzeppelin/contracts/access/Ownable.sol";
import "@openzeppelin/contracts/token/ERC20/extensions/draft-ERC20Permit.sol";


contract MyTokenC is ERC20, ERC20Burnable, Pausable, Ownable, ERC20Permit, ERC20Capped {
    constructor() ERC20("MyToken-C", "MTKC") ERC20Permit("MyToken-C") ERC20Capped(1000) {}

    function pause() public onlyOwner {
        _pause();
    }

    function unpause() public onlyOwner {
        _unpause();
    }

    function mint(address to, uint256 amount) public onlyOwner {
        _mint(to, amount);
    }

    function _mint(address account, uint256 amount) internal override(ERC20, ERC20Capped) {
        require(totalSupply() + amount <= cap(), "ERC20Capped: cap exceeded");
        super._mint(account, amount);
    }

    function _beforeTokenTransfer(address from, address to, uint256 amount)
        internal
        whenNotPaused
        override
    {
        super._beforeTokenTransfer(from, to, amount);
    }
}
3

Hey @carboncoffee,

Seems like you've figured it out. However, you're re implementing the _mint function, and although it works, you can use super.mint() with the original ERC20Capped, you can see how this plays out by referring to the Solidity Inheritance docs

The ERC20Capped receives the cap during construction, and should be used like:

contract Token is ERC20, ..., ERC20Capped {
  function _mint(address account, uint256 amount) internal override(ERC20Capped, ERC20) {
      super._mint(account, amount);
  }
}

Quick tested with the example I shared in the other thread and the cap work as expected.

Best

4

Thank you sincerely for getting back.

I deployed the contract, but the Mint function I implemented doesn't work on the main Polygon chain. When I use mint 1,000,000 the wallet balance shows as 0. ( I added the token to Metamask.) If I look at the OpenZepplin balance call it shows the balance as 1,000,000.

When I use the testnet the mint works fine. Any idea of what I did wrong?

Mint with error:

https://polygonscan.com/tx/0xf97015d40361a151741d02e1ab8a9209a89ef591063db4fc61ed996b25da7fdf

The contract is:

0xCA47A0513fe65314d018Ae3d4c5c786A8B04aB52

https://polygonscan.com/token/0xca47a0513fe65314d018ae3d4c5c786a8b04ab52?a=0x040B7eD99550906E879C86b3930bb8033D4568bf