Update Solidity version, add joint and several promisory note contract.

Author: gorankarlic

coin/Coin.sol

@@ -14,7 +14,7 @@ contract Coin is ERC20
     /**
      * Initializes the contract.
      */
-    constructor() ERC20("WHU", "WHU") public
+    constructor() ERC20("WHU", "WHU")
     {
     }
 }

liability/Joint.sol

@@ -0,0 +1,71 @@
+// SPDX-License-Identifier: MIT
+
+pragma solidity >=0.8.0 <0.9.0;
+
+/**
+ * Promissory note with joint liability.
+ */
+contract Joint
+{
+    /**
+     * Outstanding debt for each signatory.
+     */
+    uint256 public debt;
+
+    /**
+     * Signature provided for each signatory.
+     */
+    mapping(address => bool) public signed;
+
+    /**
+     * Promissory note signatories.
+     */
+    address[] public signatories;
+
+    /**
+     * Creates a new contract.
+     *
+     * @param signatories_ the promissory note signatories.
+     */
+    constructor(address[] memory signatories_) payable
+    {
+        require(msg.value % signatories_.length == 0);
+        for(uint n = 0; n < signatories_.length; n++)
+        {
+            signatories.push(signatories_[n]);
+        }
+    }
+
+    /**
+     * Accept payment of the outstanding debt in full from anyone.
+     */
+    function repay() public payable
+    {
+        require(debt == msg.value, "only accepts outstanding debt for beneficiary");
+        debt = 0;
+    }
+
+    /**
+     * Sign the promisory note.
+     */
+    function sign() public
+    {
+        signed[msg.sender] = true;
+    }
+
+    /**
+     * Withdraw the credited amount.
+     */
+    function withdraw() public
+    {
+        bool signatory = false;
+        for(uint n = 0; n < signatories.length; n++)
+        {
+            require(signed[signatories[n]], "all signatories must have signed");
+            signatory = signatory || signatories[n] == msg.sender;
+        }
+        require(signatory, "only a signatory can withdraw the credit");
+        debt = address(this).balance;
+        payable(msg.sender).transfer(address(this).balance);
+    }
+}

liability/Several.sol

@@ -0,0 +1,77 @@
+// SPDX-License-Identifier: MIT
+
+pragma solidity >=0.8.0 <0.9.0;
+
+/**
+ * Promissory note with several liability.
+ */
+contract Several
+{
+    /**
+     * Outstanding debt for each signatory.
+     */
+    mapping(address => uint256) public debt;
+
+    /**
+     * Signature provided for each signatory.
+     */
+    mapping(address => bool) public signed;
+
+    /**
+     * Promissory note signatories.
+     */
+    address[] public signatories;
+
+    /**
+     * Creates a new contract.
+     *
+     * @param signatories_ the promissory note signatories.
+     */
+    constructor(address[] memory signatories_) payable
+    {
+        require(msg.value % signatories_.length == 0);
+        for(uint n = 0; n < signatories_.length; n++)
+        {
+            signatories.push(signatories_[n]);
+        }
+    }
+
+    /**
+     * Accept payment of the proportional outstanding debt for the beneficiary.
+     *
+     * @param beneficiary the repayment beneficiary.
+     */
+    function repay(address beneficiary) public payable
+    {
+        require(debt[beneficiary] == msg.value, "only accepts outstanding debt for beneficiary");
+        debt[beneficiary] = 0;
+    }
+
+    /**
+     * Sign the promisory note.
+     */
+    function sign() public
+    {
+        signed[msg.sender] = true;
+    }
+
+    /**
+     * Withdraw the credited amount.
+     */
+    function withdraw() public
+    {
+        bool signatory = false;
+        for(uint n = 0; n < signatories.length; n++)
+        {
+            require(signed[signatories[n]], "all signatories must have signed");
+            signatory = signatory || signatories[n] == msg.sender;
+        }
+        require(signatory, "only a signatory can withdraw the credit");
+        uint256 proportion = address(this).balance / signatories.length;
+        for(uint n = 0; n < signatories.length; n++)
+        {
+            debt[signatories[n]] = proportion;
+        }
+        payable(msg.sender).transfer(address(this).balance);
+    }
+}

liability/Several_test.sol

@@ -0,0 +1,69 @@
+// SPDX-License-Identifier: MIT
+
+pragma solidity >=0.8.0 <0.9.0;
+
+import "hardhat/console.sol";
+import "remix_accounts.sol";
+import "remix_tests.sol";
+import "./Several.sol";
+
+contract SeveralTest is Several
+{
+    address creditor;
+    address signatoryA;
+    address signatoryB;
+
+    function beforeAll () public
+    {
+        creditor = TestsAccounts.getAccount(0);
+        signatoryA = TestsAccounts.getAccount(1);
+        signatoryB = TestsAccounts.getAccount(2);
+    }
+    
+    /// #sender: account-0
+    constructor(address creditor_) payable Several(testSignatories())
+    {
+        require(msg.sender == creditor_, "should have correct sender");
+        Assert.equal(msg.value, 51 ether, "should have correct value");
+    }
+
+    function testSignatories() internal pure returns (address[] memory)
+    {
+        address[] memory signatories = new address[](2);
+        signatories[0] = TestsAccounts.getAccount(1); 
+        signatories[1] = TestsAccounts.getAccount(2); 
+        return signatories;
+    }
+
+    /// #sender: account-1
+    function testSignA() public
+    {
+        Assert.equal(msg.sender, signatoryA, "should have correct sender");
+        sign();
+    }
+
+    /// #sender: account-2
+    function testSignB() public payable
+    {
+        Assert.equal(msg.sender, signatoryB, "should have correct sender");
+        sign();
+    }
+
+    /// #sender: account-1
+    function testWithdraw() public payable
+    {
+        Assert.equal(msg.sender, signatoryA, "should have correct sender");
+        uint256 initial = address(msg.sender).balance;
+        withdraw();
+        Assert.equal(address(signatoryA).balance, initial + 0 ether, "should be credited");
+    }
+
+    /// #sender: account-1
+    /// #value: 0
+    function testRepay() public payable
+    {
+        Assert.equal(msg.sender, signatoryA, "should have correct sender");
+        Assert.equal(msg.value, 0 ether, "should send 1 ether");
+        repay(signatoryA);
+    }
+}

piggybank/Piggybank.sol

@@ -23,7 +23,7 @@ contract Piggybank
     /**
      * Accept payments.
      */
-    function pay() external payable
+    receive() external payable
     {
     }
 

piggybank/Piggybank_test.sol

@@ -33,7 +33,7 @@ contract PiggybankTest is Piggybank
     {
         Assert.equal(msg.sender, grandmom, "should have correct sender");
         Assert.equal(msg.value, 5e18, "should have correct value");
-        address(piggybank).transfer(msg.value);
+        payable(address(piggybank)).transfer(msg.value);
         Assert.equal(address(piggybank).balance, msg.value, "should have some savings");
     }
 
@@ -43,7 +43,7 @@ contract PiggybankTest is Piggybank
     {
         Assert.equal(msg.sender, grandpop, "should have correct sender");
         Assert.equal(msg.value, 5e18, "should have correct value");
-        address(piggybank).transfer(msg.value);
+        payable(address(piggybank)).transfer(msg.value);
         Assert.equal(address(piggybank).balance, msg.value * 2, "should have more savings");
     }
 

web3-erc20/index.html

@@ -0,0 +1,81 @@
+<!DOCTYPE html>
+<html lang="en">
+    <head>
+        <meta charset="utf-8">
+        <meta name="viewport" content="width=device-width, initial-scale=1">
+        <title>ERC-20 Demo App</title>
+        <link crossorigin="anonymous" href="https://cdnjs.cloudflare.com/ajax/libs/fomantic-ui/2.9.0/semantic.min.css" rel="stylesheet"/>
+        <script crossorigin="anonymous" src="https://cdnjs.cloudflare.com/ajax/libs/web3/1.8.1/web3.min.js"></script>
+        <script crossorigin="anonymous" src="https://cdnjs.cloudflare.com/ajax/libs/ethers/6.8.1/ethers.umd.min.js"></script>
+    </head>
+    <body>
+        <div class="ui container">
+            <h1>ERC-20 Demo</h1>
+            <h4 class="ui dividing header">Read blockchain</h4>
+            <form class="ui form">
+                <div class="field">
+                    <div class="two fields">
+                        <div class="field">
+                            <button class="ui blue button" id="getBlockNumber" type="button">
+                                <i class="icon"></i>
+                                Get latest block number
+                            </button>
+                        </div>
+                        <div class="field">
+                            <div class="ui blue label">
+                                <i class="cube icon"></i>
+                                <a class="detail" id="blockNumber" target="_blank"></a>
+                            </div>
+                        </div>
+                    </div>
+                </div>
+            </form>
+            <br/>
+            <br/>
+            <h4 class="ui dividing header">System log</h4>
+            <pre style="color:#888"></pre>
+            <br/>
+        </div>
+        <script type="module">
+            const node = "https://eth-mainnet.gateway.pokt.network/v1/lb/29934f7f10137fb45e8609a0";
+            const provider = new ethers.JsonRpcProvider(node);
+            
+            document.querySelector("#getBlockNumber").addEventListener("click", async () =>
+            {
+                document.querySelector("#getBlockNumber i").classList.add("loading", "spinner");
+                try
+                {
+                    const blockNumber = await provider.getBlockNumber();
+                    document.querySelector("pre").textContent += `Ethereum blockchain at block number ${blockNumber}.\n`;
+                    document.querySelector("#blockNumber").href = `https://etherscan.io/block/${blockNumber}`;
+                    document.querySelector("#blockNumber").textContent = `Block number ${blockNumber}`;
+                }
+                finally
+                {
+                    document.querySelector("#getBlockNumber i").classList.remove("loading", "spinner");
+                }
+
+                const abi =
+                [
+                    "function balanceOf(address a) view returns (uint)",
+                    "function decimals() view returns (uint8)",
+                    "function symbol() view returns (string)",
+                    "function transfer(address to, uint amount)"
+                ];
+                const contract = new ethers.Contract("0xdac17f958d2ee523a2206206994597c13d831ec7", abi, provider)
+                const symbol = await contract.symbol();
+                const decimals = await contract.decimals();
+                const balance = await contract.balanceOf("ethers.eth");
+                console.log(decimals, symbol);
+
+                const wallet = new ethers.BrowserProvider(window.ethereum);
+                await wallet.send('eth_requestAccounts', []);
+                const signer = await wallet.getSigner();
+                const tx = await signer.sendTransaction({to: "ethers.eth", value: ethers.parseEther("1.0")});
+                /*const amount = ethers.parseUnits("1.0", 18);
+                const tx = await contract.transfer("ethers.eth", amount, signer);
+                await tx.wait()*/
+        });
+    </script>
+    </body>
+</html>