solidity-2.数据类型

数据类型有Value Types值类型和Reference Types引用类型

Value Types 值类型

Address 地址

长度：20 byte
注意：非address类型的数据也可以强制转换成address
address的成员
balance变量，获取地址的eth余额（单位是wei）
transfer(uint256 amount)，发送eth到一个地址，如果执行失败抛出异常，合约将停止执行
send(uint256 amount)，发送eth到一个地址，如果执行失败返回false，合约继续执行
call, callcode and delegatecall 看不懂

    address x = 0x123;
    address myAddress = this;
    if (x.balance < 10 && myAddress.balance >= 10) x.transfer(10);

Fixed-size byte arrays 固定大小字节数组

bytes1, bytes2, bytes3, …, bytes32

Enums 枚举

Function Types 函数类型

函数类型定义如下：

function (<parameter types>) {internal|external} [pure|constant|view|payable] [returns (<return types>)]

函数类型即是函数这种特殊的类型。

• 可以将一个函数赋值给一个变量，一个函数类型的变量。
• 还可以将一个函数作为参数进行传递。
• 也可以在函数调用中返回一个函数。

函数类型有两类;可分为internal和external函数。
若不写类型，默认的函数类型是internal的。

注意：
this.f 访问外部函数
f 访问内部函数

内部函数的调用：在EVM会翻译成简单的跳转指令。
外部函数的调用：不是EVM的跳转指令，而是发起一个消息调用

内部函数例子

pragma solidity ^0.4.16;

library ArrayUtils {
  // internal functions can be used in internal library functions because
  // they will be part of the same code context
  function map(uint[] memory self, function (uint) pure returns (uint) f)
    internal
    pure
    returns (uint[] memory r)
  {
    r = new uint[](self.length);
    for (uint i = 0; i < self.length; i++) {
      r[i] = f(self[i]);
    }
  }
  function reduce(
    uint[] memory self,
    function (uint, uint) pure returns (uint) f
  )
    internal
    pure
    returns (uint r)
  {
    r = self[0];
    for (uint i = 1; i < self.length; i++) {
      r = f(r, self[i]);
    }
  }
  function range(uint length) internal pure returns (uint[] memory r) {
    r = new uint[](length);
    for (uint i = 0; i < r.length; i++) {
      r[i] = i;
    }
  }
}

contract Pyramid {
  using ArrayUtils for *;
  function pyramid(uint l) public pure returns (uint) {
    return ArrayUtils.range(l).map(square).reduce(sum);
  }
  function square(uint x) internal pure returns (uint) {
    return x * x;
  }
  function sum(uint x, uint y) internal pure returns (uint) {
    return x + y;
  }
}

内部函数例子

pragma solidity ^0.4.22;

contract Oracle {
  struct Request {
    bytes data;
    function(bytes memory) external callback;
  }
  Request[] requests;
  event NewRequest(uint);
  function query(bytes data, function(bytes memory) external callback) public {
    requests.push(Request(data, callback));
    emit NewRequest(requests.length - 1);
  }
  function reply(uint requestID, bytes response) public {
    // Here goes the check that the reply comes from a trusted source
    requests[requestID].callback(response);
  }
}

contract OracleUser {
  Oracle constant oracle = Oracle(0x1234567); // known contract
  function buySomething() {
    oracle.query("USD", this.oracleResponse);
  }
  function oracleResponse(bytes response) public {
    require(
        msg.sender == address(oracle),
        "Only oracle can call this."
    );
    // Use the data
  }
}

Reference Types 引用类型

引用类型的保存比值类型要昂贵的多。

Data location 数据存储位置

• storage 永久存储
• memory 内存
• calldata 内存只读

强制数据存储位置:
没有返回参数的外部函数: calldata
合约的状态变量: storage

默认数据存储位置:
有返回值的函数: memory
局部变量: storage

arrays 数组类型

成员

length变量
push方法

• structs 结构类型
  案例如下：

pragma solidity ^0.4.11;

contract CrowdFunding {
    // Defines a new type with two fields.
    struct Funder {
        address addr;
        uint amount;
    }

    struct Campaign {
        address beneficiary;
        uint fundingGoal;
        uint numFunders;
        uint amount;
        mapping (uint => Funder) funders;
    }

    uint numCampaigns;
    mapping (uint => Campaign) campaigns;

    function newCampaign(address beneficiary, uint goal) public returns (uint campaignID) {
        campaignID = numCampaigns++; // campaignID is return variable
        // Creates new struct and saves in storage. We leave out the mapping type.
        campaigns[campaignID] = Campaign(beneficiary, goal, 0, 0);
    }

    function contribute(uint campaignID) public payable {
        Campaign storage c = campaigns[campaignID];
        // Creates a new temporary memory struct, initialised with the given values
        // and copies it over to storage.
        // Note that you can also use Funder(msg.sender, msg.value) to initialise.
        c.funders[c.numFunders++] = Funder({addr: msg.sender, amount: msg.value});
        c.amount += msg.value;
    }

    function checkGoalReached(uint campaignID) public returns (bool reached) {
        Campaign storage c = campaigns[campaignID];
        if (c.amount < c.fundingGoal)
            return false;
        uint amount = c.amount;
        c.amount = 0;
        c.beneficiary.transfer(amount);
        return true;
    }
}

Mappings 映射类型

pragma solidity ^0.4.0;

contract MappingExample {
    mapping(address => uint) public balances;

    function update(uint newBalance) public {
        balances[msg.sender] = newBalance;
    }
}

contract MappingUser {
    function f() public returns (uint) {
        MappingExample m = new MappingExample();
        m.update(100);
        return m.balances(this);
    }
}

Operators Involving LValues 运算符

一般运算符

a += e
-=, *=, /=, %=, |=, &= and ^=
a++ and a--

delete运算符，重置值/对象。

比如uint a = 10;delete a;
将a重置为0

pragma solidity ^0.4.0;

contract DeleteExample {
    uint data;
    uint[] dataArray;

    function f() public {
        uint x = data;
        delete x; // sets x to 0, does not affect data
        delete data; // sets data to 0, does not affect x which still holds a copy
        uint[] storage y = dataArray;
        delete dataArray; // this sets dataArray.length to zero, but as uint[] is a complex object, also
        // y is affected which is an alias to the storage object
        // On the other hand: "delete y" is not valid, as assignments to local variables
        // referencing storage objects can only be made from existing storage objects.
    }
}

Conversions between Elementary Types 数据类型转换

Implicit Conversions 隐式转换

address可以显示转为合约实例，同时合约实例也可以显示转换为address

MyContract contractInstance = MyContract(address mycontractAddress);
address mycontractAddress = address(contractInstance);

只能转换成比自己位数大的数据类型，比如：
uint8 转 uint16
uint160转address

Explicit Conversions 显式转换

int8 y = -3;
uint x = uint(y);

Type Deduction 未声明类型

有些时候，定义变量时没有声明数据类型，使用默认的。比如：

uint24 x = 0x123;
var y = x;

在这里，y使用var定义，它的类型将与x一致，是uint

timestamp

私有链区块时间戳案例：

• blockNumber: 0 timestamp: 0,
• blockNumber: 1 timestamp: 1526613702,
• blockNumber: 4993 timestamp: 1529483513,
• blockNumber: 4994 timestamp: 1529483514,
• blockNumber: 4995 timestamp: 1529544543,
• blockNumber: 4996 timestamp: 1529544712,
• blockNumber: 4997 timestamp: 1529544713,

block.timestamp (uint): 自 unix epoch 起始当前区块以秒计的时间戳

timestamp 以s为单位

• 1天 = 24h = 2460m = 2460*60s = 86400s
• 1小时 = 3600s
• 1分钟 = 60s