solidity语言13

函数过载

合约内允许定义同名函数，但是输入参数不一致

pragma solidity ^0.4.17;

contract A {
    function f(uint _in) public pure returns (uint out) {
        out = 1;
    }

    function f(uint _in, bytes32 _key) public pure returns (uint out) {
        out = 2;
    }
}

pragma solidity ^0.4.16;

contract A {
    function f(B _in) public pure returns (B out) {
        out = _in;
    }

    function f(address _in) public pure returns (address out) {
        out = _in;
    }
}

contract B {
}

事件

// 事件可方便使用EVM的日志工具，通过dapp的用户接口调用回调函数进行监听。

pragma solidity ^0.4.0;

contract ClientReceipt {
    event Deposit(
        address indexed _from,
        bytes32 indexed _id,
        uint _value
    );

    function deposit(bytes32 _id) public payable {
        // 任何调用当前函数的操作都会被检测到
        Deposit(msg.sender, _id, msg.value);
    }
}

var abi = /* abi as generated by the compiler */;
var ClientReceipt = web3.eth.contract(abi);
var clientReceipt = ClientReceipt.at("0x1234...ab67"); /* address */

var event = clientReceipt.Deposit();
event.watch(
    function(error, result) {
        if (!error)
            console.log(result);
});

/*或者
var event = clientReceipt.Deposit(function(error, result) {
    if (!error)
        console.log(result);
});
*/

使用log低层接口

log0, log1, log2, log3, log4 ~ logN

pragma solidity ^0.4.10;

contract C {
    function f() public payable {
        bytes32 _id = 0x420042;
        log3(
            bytes32(msg.value),
            bytes32(0x50cb9fe53daa9737b786ab3646f04d0150dc50ef4e75f59509d83667ad5adb20),
            bytes32(msg.sender),
            _id
        );
    }
}

用于理解事件的其他资源

接口

当合约继承其他合约，仅一个单独的合约被区位链建立，代码从基础合约复制到建立的合约中。

pragma solidity ^0.4.16;

contract owned {
    address owner;

    // 构造函数
    function owned() {
        owner = msg.sender;
    }
}

// 继承合约owned的所有属性，但不能使用通过this进行外部访问
contract mortal is owned {
    function kill() {
        if (msg.sender == owner)
            selfdestruct(owner);
    }
}

// These abstract contracts are only provided to make the
// interface known to the compiler. Note the function
// without body. If a contract does not implement all
// functions it can only be used as an interface.
contract Config {
    function lookup(uint id) public returns (address adr);
}

contract NameReg {
    function register(bytes32 name) public;
    function unregister() public;
}

contract named is owned, mortal {
    function named(bytes32 name) {
        Config config = Config(0xD5f9D8D94886E70b06E474c3fB14Fd43E2f23970);
        NameReg(config.lookup(1)).register(name);
    }

    function kill() public {
        if (msg.sender == owner) {
            Config config = Config(0xD5f9D8D94886E70b06E474c3fB14Fd43E2f23970);
            NameReg(config.lookup(1)).unregister();
            mortal.kill();
        }
    }
}

contract PriceFeed is owned, mortal, named("GoldFeed") {
    function updateInfo(uint newInfo) public {
        if (msg.sender == owner)
            info = newInfo;
    }

    function get() public view returns(uint r) {
        return info;
    }

    uint info;
}

pragma solidity ^0.4.0;

contract owned {
    address owner;

    function owned() public {
        owner = msg.sender;
    }
}

contract mortal is owned {
    function kill() public {
        if (msg.sender == owner)
            selfdestruct(owner);
    }
}

contract Base1 is mortal {
    function kill() public {
        /* do cleanup 1 */
        mortal.kill();
    }
}

contract Base2 is mortal {
    function kill() public {
        /* do cleanup 2 */
        mortal.kill();
    }
}

contract Final is Base1, Base2 {
}

pragma solidity ^0.4.0;

contract owned {
    function owned() public {
        owner = msg.sender;
    }

    address owner;
}

contract mortal is owned {
    function kill() public {
        if (msg.sender == owner)
            selfdestruct(owner);
    }
}

contract Base1 is mortal {
    function kill() public {
        /* do cleanup 1 */
        super.kill();
    }
}

contract Base2 is mortal {
    function kill() public {
        /* do cleanup 2 */
        super.kill(); }
}
contract Final is Base1, Base2 {
}