solidity语言14

库（Libraries）

库类似合约，实现仅在专门地址部署一次，使用EVM的DELEGATECALL的功能重复使用的目的。意思是当库函数被调用后，代码执行在被调用的合约的环境。例如，使用this调用合约，可以访问的调用合约的storage.孤立的库代码仅能访问变量，不能修改变量

pragma solidity ^0.4.16;

library Set {
    struct Data {
        mapping(uint => bool) flags;
    }

    function insert(Data storage self, uint value) public returns (bool) {
        if (self.flags[value])
            return false;

        self.flags[value] = true;
        return true;
    }

    function remove(Data storage self, uint value) public returns (bool) {
        if (!self.flags[value])
            return false;

        self.flags[value] = false;
        return true;
    }

    function contains(Data storage self, uint value) public view returns (bool) {
        return self.flags[value];
    }
}

contract C {
    Set.Data knownValues;

    function register(uint value) public {
        require(Set.insert(knownValues, value));
    }
    // In this contract, we can also directly access knownValues.flags, if we want.
}

如何使用库的memory类型和内部函数实现自定义类型，而无须使用外部方法调用

pragma solidity ^0.4.16;

library BigInt {
    struct bigint {
        uint[] limbs;
    }

    function fromUint(uint x) internal pure returns (bigint r) {
        r.limbs = new uint[](1);
        r.limbs[0] = x;
    }

    function add(bigint _a, bigint _b) internal pure returns (bigint r) {
        r.limbs = new uint[](max(_a.limbs.length, _b.limbs.length));
        uint carry = 0;

        for (uint i = 0; i < r.limbs.length; ++i) {
            uint a = limb(_a, i);
            uint b = limb(_b, i);
            r.limbs[i] = a + b + carry;

            if (a + b < a || (a + b == uint(-1) && carry > 0))
                carry = 1;
            else
                carry = 0;
        }

        if (carry > 0) {
            // too bad, we have to add a limb
            uint[] memory newLimbs = new uint[](r.limbs.length + 1);
            for (i = 0; i < r.limbs.length; ++i)
                newLimbs[i] = r.limbs[i];

            newLimbs[i] = carry;
            r.limbs = newLimbs;
        }
    }

    function limb(bigint _a, uint _limb) internal pure returns (uint) {
        return _limb < _a.limbs.length ? _a.limbs[_limb] : 0;
    }

    function max(uint a, uint b) private pure returns (uint) {
        return a > b ? a : b;
    }
}

contract C {
    using BigInt for BigInt.bigint;

    function f() public pure {
        var x = BigInt.fromUint(7);
        var y = BigInt.fromUint(uint(-1));
        var z = x.add(y);
    }
}

关键字Using For

using A for B 附加库函数A到类型B，类似python的self

using A for * 附加库函数A到所有类型

pragma solidity ^0.4.16;

library Set {
    struct Data {
        mapping(uint => bool) flags;
    }

    function insert(Data storage self, uint value) public returns (bool) {
        if (self.flags[value])
            return false; // already there

        self.flags[value] = true;
        return true;
    }

    function remove(Data storage self, uint value) public returns (bool) {
        if (!self.flags[value])
            return false; // not there

        self.flags[value] = false;
        return true;
    }

    function contains(Data storage self, uint value) public view returns (bool) {
        return self.flags[value];
    }
}

contract C {
    using Set for Set.Data; // this is the crucial change
    Set.Data knownValues;

    function register(uint value) public {
        require(knownValues.insert(value));
    }
}

使用另外方式扩展基本类型

pragma solidity ^0.4.16;

library Search {
    function indexOf(uint[] storage self, uint value) public view returns (uint) {
        for (uint i = 0; i < self.length; i++)
            if (self[i] == value) return i;
        return uint(-1);
    }
}

contract C {
    using Search for uint[];
    uint[] data;

    function append(uint value) public {
        data.push(value);
    }

    function replace(uint _old, uint _new) public {
        uint index = data.indexOf(_old);
        if (index == uint(-1))
            data.push(_new);
        else
            data[index] = _new;
    }
}