Solidity ERC-20 – Why is from Balance and Require Check Not Within Unchecked Function in Latest OpenZeppelin ERC20 Transfer?

erc-20solidity

If it is not possible to over/underflow in this transfer due to a check at the mint function, then why are these 2 lines (236/237) not within the unchecked field?

https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/contracts/token/ERC20/ERC20.sol#L236

Best Answer

Those two lines do not perform an arithmetic operation, so moving them inside the unchecked block doesn't provide any benefit. Perhaps it will make the code a little harder to read:

    uint256 fromBalance = _balances[from];
    require(fromBalance >= amount, "ERC20: transfer amount exceeds balance");
    unchecked {
        _balances[from] = fromBalance - amount;
        // Overflow not possible: the sum of all balances is capped by totalSupply, and the sum is preserved by
        // decrementing then incrementing.
        _balances[to] += amount;
    }

Related Solutions

[Ethereum] How to use 2 different constructors with open-zeppelin

ERC20Capped inherits from ERC20Mintable, which inherits from ERC20.

So if you inherit from ERC20Capped, then you don't need to inherit from ERC20.

Therefore (though without verifying it via compilation), I'm pretty sure that you can do:

contract SimpleToken is ERC20Detailed, ERC20Capped {
    uint8 public constant DECIMALS = 18;

    constructor (uint256 cap)
        ERC20Detailed("SimpleToken", "SIM", DECIMALS)
        ERC20Capped(cap)
        public {
           ...
    }
}

Solidity – What Does This Function in OpenZeppelin Address.sol Do?

It is a compatibility layer for ERC20 tokens deployed before the standard was finalized.

In the final specification function should throw in case of an error.

For transfer it says

[..] The function SHOULD throw if the message caller’s account balance does not have enough tokens to spend.

The two problems the function try to fix are:

Tokens returning false instead of throwing.
Early draft token define transfer return nothing. This clash wit newer solc version that requires the function to return a bool.

Best Answer

Related Solutions

[Ethereum] How to use 2 different constructors with open-zeppelin

Solidity – What Does This Function in OpenZeppelin Address.sol Do?

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