取引所系のトークンの特徴について

取引所系のトークンについて

• BNB, 0x, Huobi, Kucoin, Bancor, bix, kyberなどなど

UnlimitedAllowanceTokenとは

• StandardTokenを継承して、transferFromをオーバーライドしたコントラクト
• Allowanceのvalidationを追加している
  • 閾値チェック？

contract UnlimitedAllowanceToken is StandardToken {

    uint constant MAX_UINT = 2**256 - 1;
    
    /// @dev ERC20 transferFrom, modified such that an allowance of MAX_UINT represents an unlimited allowance.
    /// @param _from Address to transfer from.
    /// @param _to Address to transfer to.
    /// @param _value Amount to transfer.
    /// @return Success of transfer.
    function transferFrom(address _from, address _to, uint _value)
        public
        returns (bool)
    {
        uint allowance = allowed[_from][msg.sender];
        if (balances[_from] >= _value
            && allowance >= _value
            && balances[_to] + _value >= balances[_to]
        ) {
            balances[_to] += _value;
            balances[_from] -= _value;
            if (allowance < MAX_UINT) {
                allowed[_from][msg.sender] -= _value;
            }
            Transfer(_from, _to, _value);
            return true;
        } else {
            return false;
        }
    }
}