问工厂合同的高瓦斯成本！

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    pragma solidity >=0.4.22 <0.6.0;
    
    contract OwnedToken {
        // `TokenCreator` is a contract type that is defined below.
        // It is fine to reference it as long as it is not used
        // to create a new contract.
        TokenCreator creator;
        address owner;
        bytes32 name;
    
        // This is the constructor which registers the
        // creator and the assigned name.
        constructor(bytes32 _name) public {
            // State variables are accessed via their name
            // and not via e.g. `this.owner`. Functions can
            // be accessed directly or through `this.f`,
            // but the latter provides an external view
            // to the function. Especially in the constructor,
            // you should not access functions externally,
            // because the function does not exist yet.
            // See the next section for details.
            owner = msg.sender;
    
            // We do an explicit type conversion from `address`
            // to `TokenCreator` and assume that the type of
            // the calling contract is `TokenCreator`, there is
            // no real way to check that.
            creator = TokenCreator(msg.sender);
            name = _name;
        }
    
        function changeName(bytes32 newName) public {
            // Only the creator can alter the name --
            // the comparison is possible since contracts
            // are explicitly convertible to addresses.
            if (msg.sender == address(creator))
                name = newName;
        }
    
        function transfer(address newOwner) public {
            // Only the current owner can transfer the token.
            if (msg.sender != owner) return;
    
            // We ask the creator contract if the transfer
            // should proceed by using a function of the
            // `TokenCreator` contract defined below. If
            // the call fails (e.g. due to out-of-gas),
            // the execution also fails here.
            if (creator.isTokenTransferOK(owner, newOwner))
                owner = newOwner;
        }
    }
    
    contract TokenCreator {
        function createToken(bytes32 name)
           public
           returns (OwnedToken tokenAddress)
        {
            // Create a new `Token` contract and return its address.
            // From the JavaScript side, the return type is
            // `address`, as this is the closest type available in
            // the ABI.
            return new OwnedToken(name);
        }
    
        function changeName(OwnedToken tokenAddress, bytes32 name) public {
            // Again, the external type of `tokenAddress` is
            // simply `address`.
            tokenAddress.changeName(name);
        }
    
        // Perform checks to determine if transferring a token to the
        // `OwnedToken` contract should proceed
        function isTokenTransferOK(address currentOwner, address newOwner)
            public
            pure
            returns (bool ok)
        {
            // Check an arbitrary condition to see if transfer should proceed
            return keccak256(abi.encodePacked(currentOwner, newOwner))[0] == 0x7f;
        }
    }