Cannot mint ERC223 token - ethereum

Question

Hello I have a simple implementation for a ERC223 Token. I use this repository: ERC223-token-standard
Here is my contract Code:
pragma solidity ^0.5.8;
import "./ERC223-token-standard-development/token/ERC223/ERC223Burnable.sol";
import "./ERC223-token-standard-development/token/ERC223/ERC223Mintable.sol";
contract MyToken is ERC223Burnable, ERC223Mintable{
}
The first strange Thing is that I get this warning when compiling:
Warning: Function state mutability can be restricted to view
function mint(address account, uint256 amount) public onlyMinter returns (bool) {
^ (Relevant source part starts here and spans across multiple lines).
I think this is weird because to my understanding it changes the state of the contract and should not be a view function
However after creating my contract and using the mint function the totalSupply is still 0 even though isMinter(myaddr) returns true. I thought that I was just doing something wrong in the truffle testfile but after I pushed my code into Remix I still get the same warning and the total supply is still 0.
I hope you can help me with this issue.

Answer 1

thanks for your question, it looks like a bug in your _mint function:
function mint(address account, uint256 amount) public onlyMinter returns (bool) {
_totalSupply.add(amount);
balances[msg.sender].add(amount);
return true;
}
Let's see how add method of SafeMath lib works:
function add(uint256 a, uint256 b) internal pure returns (uint256) {
uint256 c = a + b;
require(c >= a, "SafeMath: addition overflow");
return c;
}
First of all, its pure function, which doesn't modify the state of contract. It just returns amount of addition. So, it's expected behavior for your code ‘cause you don't save a result
But if you take a look at open-zeppelin's implementation of _mint method, they change contract's state
function _mint(address account, uint256 amount) internal {
require(account != address(0), "ERC20: mint to the zero address");
_totalSupply = _totalSupply.add(amount);
_balances[account] = _balances[account].add(amount);
emit Transfer(address(0), account, amount);
}
I believe it's better to use OpenZeppelin's contracts for your development 'cause they have a lot of auditors
P.S. Also you don't use address account variable in _mint() and always add amount to msg.sender (yourself) in your implementation