upgrading to ^0.6.0; problem "Indexed expression has to be a type, mapping or array"

Question

dear Ethereum community,

I have this problem upgrading a contract from 0.4.19 to ^0.6.0:

    function someFunction(
            uint256 initialSupply,
            string memory contractName,
            string memory tokenSymbol,
            uint256 contractHoldTime,
            uint256 contractHoldMax,
            uint256 contractMaxSupply,
            address contractOwner


        ) public {

        totalSupply = initialSupply; 
        name = contractName;            
        symbol = tokenSymbol;        
        holdTime = contractHoldTime;
        holdMax = contractHoldMax;
        maxSupply = contractMaxSupply;
        owner = contractOwner; 
        balanceOf[contractOwner] = balanceOf[contractOwner].add(totalSupply);
        }

in the last line balanceOf... Indexed expression has to be a type, mapping or array (is function (address) view returns (uint256))

waiting your reply...

Thanks

Answer 1

The error means you are trying to use balanceOf as it were a mapping but it is defined as a function instead.

For OpenZeppelin 3.0 if you inherit from ERC20.sol the correct approach to modify a balance is to call _mint():

_mint(contractOwner, totalSupply);