Inheritance in Solidity

Question

contract MyToken is ERC20, ERC20Permit, ERC20Votes {
    constructor() ERC20("MyToken", "MTK") ERC20Permit("MyToken") {}

   // The following functions are overrides required by Solidity.

    function _afterTokenTransfer(address from, address to, uint256 amount)
        internal
        override(ERC20, ERC20Votes)
    {
        super._afterTokenTransfer(from, to, amount);
    }

    function _mint(address to, uint256 amount)
        internal
        override(ERC20, ERC20Votes)
    {
        super._mint(to, amount);
    }

    function _burn(address account, uint256 amount)
        internal
        override(ERC20, ERC20Votes)
    {
        super._burn(account, amount);
    }
}

Can somebody explain why we need to override these 4 functions from base contract ? It's not possible to call it from super keyword?

score 0 · Accepted Answer · answered Feb 20 '23 at 15:47

I will explain on this

 function _afterTokenTransfer(address from, address to, uint256 amount)
        internal
        override(ERC20, ERC20Votes)
    {
        super._afterTokenTransfer(from, to, amount);
    }

Normally, super._afterTokenTransfer will check parent contracts, find _afterTokenTransfer function and call it. But if your contract is inheriting from multiple contracts, and more than one contract has the same function, it will inherit from the right-most contract first. But since you have this:

 override(ERC20, ERC20Votes)

it will visit both the contract and call _afterTokenTransfer inside each contract. If you did not have this override(ERC20, ERC20Votes)

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

since the right-most parent contract is ERC20Votes, super._afterTokenTransfer(from, to, amount) this will call only from ERC20Votes

Inheritance in Solidity

1 Answers1