`CheckContract` for token contracts

[abhi3700]

Instead of this line, the check contract logic can be written by introducing a function like this:

/**
 * Check that the account is an already deployed non-destroyed contract.
 * See: https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/contracts/utils/Address.sol#L12
 */
function _checkContract(address _account) private view {
    require(_account != address(0), "Account cannot be zero address");

    uint256 size;
    // solhint-disable-next-line no-inline-assembly
    assembly {
        size := extcodesize(_account)
    }
    require(size != 0, "Account code size cannot be zero");
}

[hacklili]

what

[abhi3700]

this is to check whether the parsed contract address has some ERC20 code.

this is not recommended because

1. It blocks developers creating a pair before deploying a token contract ( some may find this useful )

2. Every pair liquidity is dedicated so if the pair token isn't deployed or doesn't fulfill ERC20 standard core functionality wouldn't work including providing liquidity, etc. so it doesn't matter.