Two or more base classes define function with same name and parameter types

Question

// SPDX-License-Identifier: MIT

pragma solidity ^0.8.19;

import "@openzeppelin/contracts/token/ERC20/ERC20.sol";
import "@openzeppelin/contracts/token/ERC20/extensions/ERC20Capped.sol";
import "@openzeppelin/contracts/token/ERC20/extensions/ERC20Burnable.sol";

contract GNaira is ERC20, ERC20Capped, ERC20Burnable {
    address public owner;

    constructor(uint256 cap) ERC20("GNaira", "gNGN") ERC20Capped(cap * (10 ** decimals())) {
        owner = msg.sender;
        _mint(owner, 3000000000000 * (10 ** decimals())); // Mint initial supply up to the cap
    }

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

    function _beforeTokenTransfer(address from, address to, uint256 amount)
        internal
        override(ERC20, ERC20Capped, ERC20Burnable)
    {
        super._beforeTokenTransfer(from, to, amount);
    }
}

// SPDX-License-Identifier: MIT

pragma solidity ^0.8.19;

import "@openzeppelin/contracts/token/ERC20/ERC20.sol";
import "@openzeppelin/contracts/token/ERC20/extensions/ERC20Capped.sol";
import "@openzeppelin/contracts/token/ERC20/extensions/ERC20Burnable.sol";

contract GNaira is ERC20Capped, ERC20Burnable {
    address public owner;

    constructor(
        uint256 cap
    ) ERC20("GNaira", "gNGN") ERC20Capped(cap * (10 ** decimals())) {
        owner = msg.sender;
        _mint(owner, 3000000000000 * (10 ** decimals()));
    }
}

The code below was the initial code. The code above was recommended as a solution and it still showing the same error. How do I fix it? I'd appreciate the help.

Answer 1

This is because both of the contracts you are inheriting are inherited from ERC20 itself.

This code should work, as you need to override the _update function only.

import "@openzeppelin/contracts/token/ERC20/ERC20.sol";
import "@openzeppelin/contracts/token/ERC20/extensions/ERC20Capped.sol";
import "@openzeppelin/contracts/token/ERC20/extensions/ERC20Burnable.sol";

contract GNaira is ERC20, ERC20Capped, ERC20Burnable {
    address public owner;

    constructor(uint256 cap) ERC20("GNaira", "gNGN") ERC20Capped(cap * (10 ** decimals())) {
        owner = msg.sender;
        _mint(owner, 3000000000000 * (10 ** decimals())); // Mint initial supply up to the cap
    }

    function _update(address from, address to, uint256 value)
        internal
        override(ERC20,ERC20Capped)
    {
        super._update(from, to, value);
    }
}

This should work as expected.