Lecture 5 - Homework & Resources

kao-zai · 10 March 2021 07:41

1 Videos

01 - Example: CourseCoin (25:56)
02 - Example: TimeLockedTransfer (15:53)

total duration: 41:49

2 Resources

Conflux Studio Project (unzip, then import into Conflux Studio)
github.com/Thegaram/cfx-uma-resources/raw/master/cfx-lecture-5.zip

Submit bugs and feature requests to Conflux Studio

Official Solidity 7.1 documentation
solidity.readthedocs.io/en/v0.7.1

OpenZeppelin ERC-20 interface

github.com

OpenZeppelin/openzeppelin-contracts/blob/master/contracts/token/ERC20/IERC20.sol

// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

/**
 * @dev Interface of the ERC20 standard as defined in the EIP.
 */
interface IERC20 {
    /**
     * @dev Returns the amount of tokens in existence.
     */
    function totalSupply() external view returns (uint256);

    /**
     * @dev Returns the amount of tokens owned by `account`.
     */
    function balanceOf(address account) external view returns (uint256);

    /**
     * @dev Moves `amount` tokens from the caller's account to `recipient`.

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OpenZeppelin ERC-20 implementation

github.com

OpenZeppelin/openzeppelin-contracts/blob/master/contracts/token/ERC20/ERC20.sol

// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

import "./IERC20.sol";
import "./extensions/IERC20Metadata.sol";
import "../../utils/Context.sol";

/**
 * @dev Implementation of the {IERC20} interface.
 *
 * This implementation is agnostic to the way tokens are created. This means
 * that a supply mechanism has to be added in a derived contract using {_mint}.
 * For a generic mechanism see {ERC20PresetMinterPauser}.
 *
 * TIP: For a detailed writeup see our guide
 * https://forum.zeppelin.solutions/t/how-to-implement-erc20-supply-mechanisms/226[How
 * to implement supply mechanisms].
 *
 * We have followed general OpenZeppelin guidelines: functions revert instead

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ERC-20 (Bitcoin Wiki)

3 Homeworks

3.1 Undertanding the lecture

1.a) Describe some advantages of conforming to a token standard like ERC-20 or IStandardToken in a few sentences.
1.b) Describe the purpose of the TimeLockedTransfer contract in a few sentences.

3.2 Trying the lecture code

Download the project (github.com/Thegaram/cfx-uma-resources/raw/master/cfx-lecture-5.zip) and import it into Conflux Studio.

In this problem, you will have to deploy three smart contracts on your local development network.

First, deploy a fixed-supply standard coin with the name “CoinA”. Then, deploy a second instance with the name “CoinB”.

Next, deploy an instance of the TimeLockedTransfer contract. Set the unlock time to something greater than 5 minutes.

Send 17 CFX, 22 CoinA, and 12 CoinB to the transfer contract.

After the deadline, withdraw all these tokens from the transfer contract.

Document the process using screenshots and a short description of each step.

+1. Transfer Factory [OPTIONAL]

Look at the file TransferFactory.sol. Try to understand what it does and explain it using your own words.

Show us how to deploy and use this contract.

+1. Cancel transfer [OPTIONAL]

Modify TimeLockedTransfer.sol in a way that allows the sender to cancel the transfer before the specified deadline.

Provide a way for the sender to re-aquire all their tokens from the transfer contract after cancelling it.