Unit 20 – “Looks like we’ve made our first contract!”

Background

Your new startup has created its own Ethereum-compatible blockchain to help connect financial institutions, and the team wants to build smart contracts to automate some company finances to make everyone’s lives easier, increase transparency, and to make accounting and auditing practically automatic.

Fortunately, you’ve been learning how to program smart contracts with Solidity! What you will be doing this assignment is creating a few ProfitSplitter contracts. These contracts will do several things:

• Pay your associate-level employees quickly and easily.

• Distribute profits to different tiers of employees.

• Distribute company shares for employees in a “deferred equity incentive plan” automatically.

Files

• AssociateProfitSplitter.sol — Level 1 starter code.

• TieredProfitSplitter.sol — Level 2 starter code.

• DeferredEquityPlan.sol — Level 3 starter code.

Instructions

This assignment has three levels of difficulty, with each contract increasing in complexity and capability. Start with Level 1, and then move forward as you complete the challenges. You can build all three with the skills you already have!

• Level One is an AssociateProfitSplitter contract. This will accept ether into the contract, and divide it evenly among associate-level employees. This will allow the human resources department to pay employees quickly and efficiently.

• Level Two is a TieredProfitSplitter that will distribute different percentages of incoming ether to employees at different tiers/levels. For example, the CEO gets paid 60%, CTO 25%, and Bob gets 15%.

• Level Three is a DeferredEquityPlan that models traditional company stock plans. This contract will automatically manage 1000 shares, with an annual distribution of 250 shares over four years for a single employee.

Starting your project

Navigate to the Remix IDE and create a new contract called AssociateProfitSplitter.sol using the starter code for Level One above.

While developing and testing your contract, use the Ganache development chain, and point MetaMask to localhost:8545, or replace the port with what you have set in your workspace.

Level One: The AssociateProfitSplitter Contract

At the top of your contract, you will need to define the following public variables:

• employee_one — The address of the first employee. Make sure to set this to payable.

• employee_two — Another address payable that represents the second employee.

• employee_three — The third address payable that represents the third employee.

Create a constructor function that accepts:

• address payable _one

• address payable _two

• address payable _three

Within the constructor, set the employee addresses to equal the parameter values. This will allow you to avoid hardcoding the employee addresses.

Next, create the following functions:

• balance — This function should be set to public view returns(uint), and must return the contract’s current balance. Since we should always be sending ether to the beneficiaries, this function should always return 0. If it does not, the deposit function is not handling the remainders properly and should be fixed. This will serve as a test function of sorts.

• deposit — This function should be set to public payable check, ensuring that only the owner can call the function.

  • In this function, perform the following steps:

    • Set a uint amount to equal msg.value / 3; in order to calculate the split value of the ether.

    • Transfer the amount to employee_one.

    • Repeat the steps for employee_two and employee_three.

    • Since uint only contains positive whole numbers, and Solidity does not fully support float/decimals, we must deal with a potential remainder at the end of this function, since amount will discard the remainder during division.

    • We may either have 1 or 2 wei left over, so transfer the msg.value - amount * 3 back to msg.sender. This will re-multiply the amount by 3, then subtract it from the msg.value to account for any leftover wei, and send it back to human resources.

• Create a fallback function using function() external payable, and call the deposit function from within it. This will ensure that the logic in deposit executes if ether is sent directly to the contract. This is important to prevent ether from being locked in the contract, since we don’t have a withdraw function in this use case.

Test the contract

In the Deploy tab in Remix, deploy the contract to your local Ganache chain by connecting to Injected Web3 and ensuring MetaMask is pointed to localhost:8545.

You will need to fill in the constructor parameters with your designated employee addresses.

Test the deposit function by sending various values. Keep an eye on the employee balances as you send different amounts of ether to the contract and ensure the logic is executing properly.

Level Two: The TieredProfitSplitter Contract

In this contract, rather than splitting the profits between associate-level employees, you will calculate rudimentary percentages for different tiers of employees (CEO, CTO, and Bob).

Using the starter code, within the deposit function, perform the following:

• Calculate the number of points/units by dividing msg.value by 100.

  • This will allow us to multiply the points with a number representing a percentage. For example, points * 60 will output a number that is ~60% of the msg.value.

• The uint amount variable will be used to store the amount to send each employee temporarily. For each employee, set the amount to equal the number of points multiplied by the percentage (say, 60 for 60%).

• After calculating the amount for the first employee, add the amount to the total to keep a running total of how much of the msg.value we are distributing so far.

• Then, transfer the amount to employee_one. Repeat the steps for each employee, setting the amount to equal the points multiplied by their given percentage.

• For example, each transfer should look something like the following for each employee, until after transferring to the third employee:

  • Step 1: amount = points * 60;

    • For employee_one, distribute points * 60.

    • For employee_two, distribute points * 25.

    • For employee_three, distribute points * 15.

  • Step 2: total += amount;

  • Step 3: employee_one.transfer(amount);

• Send the remainder to the employee with the highest percentage by subtracting total from msg.value, and sending that to an employee.

• Deploy and test the contract functionality by depositing various ether values (greater than 100 wei).

  • The provided balance function can be used as a test to see if the logic you have in the deposit function is valid. Since all of the ether should be transferred to employees, this function should always return 0, since the contract should never store ether itself.

  • Note: The 100 wei threshold is due to the way we calculate the points. If we send less than 100 wei, for example, 80 wei, points would equal 0 because 80 / 100 equals 0 because the remainder is discarded. We will learn more advanced arbitrary precision division later in the course. In this case, we can disregard the threshold as 100 wei is a significantly smaller value than the ether or Gwei units that are far more commonly used in the real world (most people aren’t sending less than a penny’s worth of ether).

Level Three: The DeferredEquityPlan Contract

In this contract, we will be managing an employee’s “deferred equity incentive plan,” in which 1000 shares will be distributed over four years to the employee. We won’t need to work with ether in this contract, but we will be storing and setting amounts that represent the number of distributed shares the employee owns, and enforcing the vetting periods automatically.

• A two-minute primer on deferred equity incentive plans: In this set-up, employees receive shares for joining and staying with the firm. They may receive, for example, an award of 1000 shares when joining, but with a four-year vesting period for these shares. This means that these shares would stay with the company, with only 250 shares (1000/4) actually distributed to and owned by the employee each year. If the employee leaves within the first four years, he or she would forfeit ownership of any remaining (“unvested”) shares.

  • If, for example, the employee only sticks around for the first two years before moving on, the employee’s account will end up with 500 shares (250 shares * 2 years), with the remaining 500 shares staying with the company. In this example, only half of the shares (and any distributions of company profit associated with them) actually “vested,” or became fully owned by the employee. The remaining half, which were still “deferred” or “unvested,” ended up fully owned by the company since the employee left midway through the incentive/vesting period.

  • Specific vesting periods, the dollar/crypto value of shares awarded, and the percentage equity stake (the percentage ownership of the company) all tend to vary according to the company, the specialized skills, or seniority of the employee, and the negotiating positions of the employee/company. If you receive an offer from a company offering equity (which is great!), just make sure you can clarify the current dollar value of those shares being offered (based on, perhaps, valuation implied by the most recent outside funding round). In other words, don’t be content with just receiving “X” number of shares without having a credible sense of what amount of dollars that “X” number represents. Be sure to understand your vesting schedule as well, particularly if you think you may not stick around for an extended period of time.

Using the starter code, perform the following:

• Human resources will be set in the constructor as the msg.sender, since HR will be deploying the contract.

• Below the employee initialization variables at the top (after bool active = true;), set the total shares and annual distribution:

  • Create a uint called total_shares and set this to 1000.

  • Create another uint called annual_distribution and set this to 250. This equates to a four-year vesting period for the total_shares, as 250 will be distributed per year. Since it is expensive to calculate this in Solidity, we can simply set these values manually. You can tweak them as you see fit, as long as you can divide total_shares by annual_distribution evenly.

• The uint start_time = now; line permanently stores the contract’s start date. We’ll use this to calculate the vested shares later. Below this variable, set the unlock_time to equal now plus 365 days. We will increment each distribution period.

• The uint public distributed_shares will track how many vested shares the employee has claimed and were distributed. By default, this is 0.

• In the distribute function:

  • Add the following require statements:

    • Require that unlock_time is less than, or equal to, now.

    • Require that distributed_shares is less than the total_shares the employee was set for.

    • Ensure to provide error messages in your require statements.

  • After the require statements, add 365 days to the unlock_time. This will calculate next year’s unlock time before distributing this year’s shares. We want to perform all of our calculations like this before distributing the shares.

  • Next, set the new value for distributed_shares by calculating how many years have passed since start_time multiplied by annual_distributions. For example:

    • The distributed_shares is equal to (now - start_time) divided by 365 days, multiplied by the annual distribution. If now - start_time is less than 365 days, the output will be 0 since the remainder will be discarded. If it is something like 400 days, the output will equal 1, meaning distributed_shares would equal 250.

    • Make sure to include the parenthesis around now - start_time in your calculation to ensure that the order of operations is followed properly.

  • The final if statement provided checks in the case the employee does not cash out until 5+ years after the contract start, the contract does not reward more than the total_shares agreed upon in the contract.

• Deploy and test your contract locally.

  • For this contract, test the timelock functionality by adding a new variable called uint fakenow = now; as the first line of the contract, then replace every other instance of now with fakenow. Utilize the following fastforward function to manipulate fakenow during testing.

  • Add this function to “fast forward” time by 100 days when the contract is deployed (requires setting up fakenow):

    function fastforward() public {     fakenow += 100 days; }

  • Once you are satisfied with your contract’s logic, revert the fakenow testing logic.

• Congratulate yourself for building such complex smart contracts in your first week of Solidity! You are learning specialized skills that are highly desired in the blockchain industry!

Deploy the contracts to a live Testnet

Once you feel comfortable with your contracts, point MetaMask to the Kovan or Ropsten network. Make sure that you have test ether on this network!

After switching MetaMask to Kovan, deploy the contracts as before, and copy/keep a note of their deployed addresses. The transactions will also be in your MetaMask history, and on the blockchain permanently to explore later.

Resources

Building the next financial revolution isn’t easy, but we need your help. Don’t be intimidated by the semicolons!

There are lots of great resources to learn Solidity. Remember, you are helping push the very edge of this space forward, so don’t feel discouraged if you get stuck! In fact, be proud that you are taking on such a challenge!

For some succinct and straightforward code snips, check out Solidity By Example

For a more extensive list of awesome Solidity resources, check out Awesome Solidity

Another tutorial is available at EthereumDev.io

If you enjoy building games, here’s an excellent tutorial called CryptoZombies

Submission

Create a README.md that explains what testnet the contract is on, the motivation for the contract.

Upload this to a Github repository that explains how the contract works, and provide the testnet address for others to be able to send to.

© 2020 Trilogy Education Services, a 2U, Inc. brand. All Rights Reserved.

Unit 20 – “Looks like we’ve made our first contract!”

Background

您的新公司创建了自己的以太坊eth兼容区块链blockchain，以帮助连接金融机构，团队希望构建智能合约，使公司财务自动化，使每个人的生活更轻松，增加透明度，并使会计和审计几乎自动化。

幸运的是，您已经学会了如何用Solidity编写智能合约！你要做的是创建一些ProfitSplitter合同。这些合同可以做几件事：

• 快速、轻松地支付助理级员工的工资。

• 将利润分配给不同级别的员工。

• 自动为“递延股权激励计划”中的员工分配公司股票。

Files

• 屁股SociateProfitSplitter.sol-1级起动机代码。

• 分层ProfitSplitter.sol-起动机代码2。

• 延迟QuityPlan.sol-3级起动机代码。

Instructions

这项任务有三个难度，每项合同的复杂性和能力都在增加。从第1级开始，然后在完成挑战时继续前进。你可以用你已经掌握的技能来建造这三个！

• 第一级是AssociateProfitPlitter合同。这将接受以太合同，并将其平均分配给副员工。这将使人力资源部能够迅速有效地支付员工工资。

• 第二级是一个分层ProfitSplitter，它将向不同级别/级别的员工分配不同百分比的入职乙醚。例如，首席执行官的薪酬为60%，首席技术官的薪酬为25%，鲍勃的薪酬为15%。

• 第三级是一种延迟收益计划，它模拟了传统的公司股票计划。这项合同将自动管理1000股，每名员工在四年内每年分配250股。

Starting your project

导航到Remix IDE并创建一个名为Ass的新合同SociateProfitSplitter.sol使用以上一级的启动程序代码。

在开发和测试合同时，使用Ganache开发链，并将MetaMask指向本地主机：8545，或将端口替换为您在工作区中设置的端口。

Level One: The AssociateProfitSplitter Contract

在合同顶部，您需要定义以下公共变量：

• employee_one-第一个员工的地址。请确保将此设置为“应付”。

• employee_two-代表第二名员工的另一个应付地址。

• employee_three-代表第三名员工的第三个应付地址。

创建一个构造函数函数，该函数接受：

• 应付地址

• 应付地址

• 应付地址三

在构造函数中，将员工地址设置为等于参数值。这样可以避免对员工地址进行硬编码。

接下来，创建以下函数：

• 余额-此函数应设置为public view returns（uint），并且必须返回合同的当前余额。因为我们应该总是向受益人发送以太，所以这个函数应该总是返回0。如果没有，那么存款功能就不能正确地处理剩余部分，应该加以修正。这将作为某种测试功能。

• 存款-此函数应设置为公共应付支票，以确保只有所有者可以调用该函数。

  • 在此函数中，执行以下步骤：

    • 将uint amount设置为相等消息值/3；以计算乙醚的拆分值。

    • 将金额转移到员工1。

    • 对员工2和员工3重复上述步骤。

    • 由于uint只包含正整数，而Solidity不完全支持浮点/小数，因此我们必须在函数末尾处理一个可能的余数，因为amount将在除法过程中丢弃余数。

    • 我们可能还剩下1或2个wei，所以转移消息值-金额*3返回消息发送者. 这将把数量乘以3，然后从消息值核算任何剩余的小威，并将其发回人力资源部。

• 使用function（）external payment创建一个回退函数，并从其中调用deposit函数。这将确保如果ether被直接发送到合同，那么deposit中的逻辑将得到执行。这对于防止ether被锁定在合同中是很重要的，因为我们在这个用例中没有撤销功能。

Test the contract

在Remix的Deploy选项卡中，通过连接到注入的Web3并确保指向MetaMask，将契约部署到本地的Ganache链本地主机：8545。

您需要用指定的员工地址填写构造函数参数。

通过发送不同的值来测试deposit函数。在向合同发送不同数量的乙醚时，请注意员工余额，并确保逻辑正确执行。

Level Two: The TieredProfitSplitter Contract

在本合同中，您将计算不同级别员工（CEO、CTO和Bob）的基本百分比，而不是在助理级别员工之间分配利润。使用

• 除法计算

  • This will allow us to multiply the points with a number representing a percentage. For example, points * 60 will output a number that is ~60% of the msg.value.

• 起始单位内的存款点数消息值到100岁。

• uint amount变量将用于存储临时发送给每个员工的金额。对于每个员工，将金额设置为点数乘以百分比（例如，60%为60%）。

• 计算完第一个员工的金额后，将该金额添加到总额中，以保持消息值我们目前正在分发。

• 然后，将金额转移到员工1。对每个员工重复这些步骤，将金额设置为点数乘以他们给定的百分比。

  • 例如，对于每个员工，每次调动都应该类似于以下内容，直到转移到第三个员工之后：

    • 第1步：amount=points*60；

    • 对于员工1，分配积分*60。

    • 对于第二名员工，分配25分。

  • 对于第三名员工，分配15分。

  • 第2步：合计+=金额；

• 第3步：员工_一、转让（amount）；

• 将余额减去消息值然后把它发给一个雇员。

  • 通过存储各种以太值（大于100 wei）来部署和测试契约功能。

  • 所提供的余额函数可用于测试存款函数中的逻辑是否有效。因为所有的ether都应该被转移到employees，所以这个函数应该总是返回0，因为契约本身不应该存储ether。

Level Three: The DeferredEquityPlan Contract

注意：100wei阈值取决于我们计算点数的方式。如果我们发送的数据小于100wei，例如80wei，那么点数将等于0，因为80/100等于0，因为余数被丢弃。我们将在后面的课程中学习更高级的任意精度除法。在这种情况下，我们用的价值远远低于以太币的价值。

• 在本合同中，我们将管理员工的“递延股权激励计划”，其中1000股股票将在4年内分配给员工。我们不需要在这个合同中使用ether，但我们将存储和设置代表员工拥有的已分配股份数量的金额，并自动执行审核周期。

  • 延迟股权激励计划的两分钟入门课程：在这一设置中，员工因加入和留在公司而获得股份。例如，他们在加入时可以获得1000股的奖励，但这些股票的授予期为4年。这意味着这些股份将留在公司，每年只有250股（1000/4）的股份实际分配给员工并由其拥有。如果雇员在头四年内离职，他或她将丧失任何剩余（“未行权”）股份的所有权。

  • 例如，如果员工只在离职前的前两年留下来，那么员工的账户最终将持有500股（250股*2年），剩下的500股将留在公司。在这个例子中，只有一半的股份（以及与之相关的公司利润分配）实际上“归属”或完全由员工拥有。剩下的一半，仍然是“延期”或“未授予”的，由于员工在激励/授予期中途离职，最终全部归公司所有。

具体的授予期、授予股份的美元/加密价值以及股权比例（公司所有权百分比）都会因公司、员工的专业技能或资历以及员工/公司的谈判立场而有所不同。如果你收到一家提供股票的公司的报价（那太好了！），只需确保你能澄清所发行股票的当前美元价值（可能基于最近一轮外部融资所暗示的估值）。换言之，不要满足于仅仅得到“X”数量的股票，而不知道“X”数字代表多少美元。一定要了解你的行权时间表，特别是如果你认为你可能不会坚持很长一段时间。

• 使用启动程序代码，执行以下操作：

• 人力资源将在构造函数中设置为消息发送者，因为HR将部署合同。

  • 在顶部的employee初始化变量下面（bool active=true；）设置总股份和年度分配：

  • 创建一个名为total_shares的uint并将其设置为1000。

• 创建另一个名为“年度分配”的uint，并将其设置为250。这个e

• The uint public distributed_shares will track how many vested shares the employee has claimed and were distributed. By default, this is 0.

• In the distribute function:

  • Add the following require statements:

    • Require that unlock_time is less than, or equal to, now.

    • Require that distributed_shares is less than the total_shares the employee was set for.

    • Ensure to provide error messages in your require statements.

  • After the require statements, add 365 days to the unlock_time. This will calculate next year’s unlock time before distributing this year’s shares. We want to perform all of our calculations like this before distributing the shares.

  • Next, set the new value for distributed_shares by calculating how many years have passed since start_time multiplied by annual_distributions. For example:

    • The distributed_shares is equal to (now - start_time) divided by 365 days, multiplied by the annual distribution. If now - start_time is less than 365 days, the output will be 0 since the remainder will be discarded. If it is something like 400 days, the output will equal 1, meaning distributed_shares would equal 250.

    • Make sure to include the parenthesis around now - start_time in your calculation to ensure that the order of operations is followed properly.

  • The final if statement provided checks in the case the employee does not cash out until 5+ years after the contract start, the contract does not reward more than the total_shares agreed upon in the contract.

• Deploy and test your contract locally.

  • For this contract, test the timelock functionality by adding a new variable called uint fakenow = now; as the first line of the contract, then replace every other instance of now with fakenow. Utilize the following fastforward function to manipulate fakenow during testing.

  • Add this function to “fast forward” time by 100 days when the contract is deployed (requires setting up fakenow):

    function fastforward() public {     fakenow += 100 days; }

  • Once you are satisfied with your contract’s logic, revert the fakenow testing logic.

• Congratulate yourself for building such complex smart contracts in your first week of Solidity! You are learning specialized skills that are highly desired in the blockchain industry!

Deploy the contracts to a live Testnet

Once you feel comfortable with your contracts, point MetaMask to the Kovan or Ropsten network. Make sure that you have test ether on this network!

After switching MetaMask to Kovan, deploy the contracts as before, and copy/keep a note of their deployed addresses. The transactions will also be in your MetaMask history, and on the blockchain permanently to explore later.

Resources

Building the next financial revolution isn’t easy, but we need your help. Don’t be intimidated by the semicolons!

There are lots of great resources to learn Solidity. Remember, you are helping push the very edge of this space forward, so don’t feel discouraged if you get stuck! In fact, be proud that you are taking on such a challenge!

For some succinct and straightforward code snips, check out Solidity By Example

For a more extensive list of awesome Solidity resources, check out Awesome Solidity

Another tutorial is available at EthereumDev.io

If you enjoy building games, here’s an excellent tutorial called CryptoZombies

Submission

Create a README.md that explains what testnet the contract is on, the motivation for the contract.

Upload this to a Github repository that explains how the contract works, and provide the testnet address for others to be able to send to.

© 2020 Trilogy Education Services, a 2U, Inc. brand. All Rights Reserved.