Intro to Ether programming

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合约方法

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progma solidity ^0.4.0;
contract SimpleStorage{
  uint storedData;
  function set(uint x){
    storedData = x;
  }
  function get() constant returns(uint){
    return storedData;
  }
}

写程序费用按照gas给挖矿者， gas != Ether
使得函数调用成本相对稳定

背景介绍

  • 传统的员工系统
  • 整型UINT/INT
    （不存在float，不支持）
  • 地址 Address
    • address.balance
    • address.transfer(value)
    • address.send(value)
    • address.call, address.callcode and address.delegatecall

设计

  1. 薪水将全部基于Ethereum
    • uint salary
    • address frank
      2.
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contract Payroll {
  uint salary = 1 ether;
  address frank = sample_address;
  uint constant Duration = 30 days;
  uint lastPayday = now;
  <!-- function test(){
    payDuration = 1 days;
  } -->
  function addFund() payable return(uint){
      return this.balance;  // `this` is an address type
  }
  function calculateRunway() return(uint){
    return this.balance / salary;
  }
  function hasEnoughFund() return(bool){
    // return this.balance >= salary;
    return calculateRunway() > 0;
    // gas assumption is far less than this.calculateRunway() (use msg)
  }
  function getPaid() {
    if(msg.sender != bob){
      revert();
    }
    uint nextPayDay = lastPayday + payDuration;
    if (nextPayDay > now){
      revert();// instead of throw
    }
    lastPayday = nextPayDay;
    frank.transfer(salary);
    // change interval variable => transfer money (to avoid re-enter attack)
    // no compiler optimization yet
    // scope of local defined variable is global
  }
}

ETHER unit （只是方便ti数字替代）

  • wei
  • szabo = 10^12 wei
  • find
  • ether = 10^18 wei

e.g. 1 wei == 1
时间单位

h2.Block

  • block.blockhash
  • block.coinbase
  • block.difficulty(uint)
  • block.

h2.Message

  • msg.data
  • msg.gas(uint)
  • msg.sender(address)
  • msg.sig
  • msg.value(uint)

如何发放薪水
（函数被动调用）

  • 定时器？
  • Bob send money to Alice by contract
  • How to prevent Bob from not giving Alice the money
  • Save money in smart contract, and Alice get money every 30 days
    • function addFund
    • function calculateRunway
    • function hasEnoughFund
    • function getPaid