ERC20approve.sol

/* Bad */
function approve(address _spender, uint256 _value) public returns (bool success) {
    _allowances[msg.sender][_spender] = _value
}
/* Better */
import "@openzeppelin/contracts/token/ERC20/utils/SafeERC20.sol";
SafeERC20 for IERC20;
IERC20 token;

function addAllowance(IERC20 _token,address _spender, uint256 _value) public returns (bool success) {
    token.safeIncreaseAllowance(_token, _spender, _value);
}

function decreaseAllowance(address _spender, uint256 _value) public returns (bool success) {
    token.safeDecreaseAllowance(_token, _spender, _value);
}