solidity–erc720

Any contract that follow the ERC20 standard is a ERC20 token.

ERC20 tokens provide functionalities to

transfer tokens
allow others to transfer tokens on behalf of the token holder

Here is the interface for ERC20.

任何遵循 ERC20 标准的合约都是 ERC20 代币。

ERC20 代币提供以下功能

转移代币
允许其他人代表代币持有者转移代币

这是ERC20的接口。

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.13;

// https://github.com/OpenZeppelin/openzeppelin-contracts/blob/v3.0.0/contracts/token/ERC20/IERC20.sol
interface IERC20 {
function totalSupply() external view returns (uint);

function balanceOf(address account) external view returns (uint);

function transfer(address recipient, uint amount) external returns (bool);

function allowance(address owner, address spender) external view returns (uint);

function approve(address spender, uint amount) external returns (bool);

    function transferFrom(
        address sender,
        address recipient,
        uint amount
    ) external returns (bool);

event Transfer(address indexed from, address indexed to, uint value);
event Approval(address indexed owner, address indexed spender, uint value);
}

example

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.13;

import "./IERC20.sol";

contract ERC20 is IERC20 {
    uint public totalSupply;
    mapping(address => uint) public balanceOf;
    mapping(address => mapping(address => uint)) public allowance;
    string public name = "Solidity by Example";
    string public symbol = "SOLBYEX";
    uint8 public decimals = 18;

    function transfer(address recipient, uint amount) external returns (bool) {
        balanceOf[msg.sender] -= amount;
        balanceOf[recipient] += amount;
        emit Transfer(msg.sender, recipient, amount);
        return true;
    }

    function approve(address spender, uint amount) external returns (bool) {
        allowance[msg.sender][spender] = amount;
        emit Approval(msg.sender, spender, amount);
        return true;
    }

    function transferFrom(
        address sender,
        address recipient,
        uint amount
    ) external returns (bool) {
        allowance[sender][msg.sender] -= amount;
        balanceOf[sender] -= amount;
        balanceOf[recipient] += amount;
        emit Transfer(sender, recipient, amount);
        return true;
    }

    function mint(uint amount) external {
        balanceOf[msg.sender] += amount;
        totalSupply += amount;
        emit Transfer(address(0), msg.sender, amount);
    }

    function burn(uint amount) external {
        balanceOf[msg.sender] -= amount;
        totalSupply -= amount;
        emit Transfer(msg.sender, address(0), amount);
    }
}

Create your own ERC20 token

Using Open Zeppelin it's really easy to create your own ERC20 token.

Here is an example

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.13;

import "https://github.com/OpenZeppelin/openzeppelin-contracts/blob/v4.0.0/contracts/token/ERC20/ERC20.sol";

contract MyToken is ERC20 {
    constructor(string memory name, string memory symbol) ERC20(name, symbol) {
        // Mint 100 tokens to msg.sender
        // Similar to how
        // 1 dollar = 100 cents
        // 1 token = 1 * (10 ** decimals)
        _mint(msg.sender, 100 * 10**uint(decimals()));
    }
}

Contract to swap tokens

Here is an example contract,

TokenSwap

, to trade one ERC20 token for another.

This contract will swap tokens by calling

transferFrom(address sender, address recipient, uint256 amount)

which will transfer

amount

of token from

sender

recipient

For

transferFrom

to succeed,

sender

must

have more than
```
amount
```
tokens in their balance
allowed
```
TokenSwap
```
to withdraw
```
amount
```
tokens by calling
```
approve
```

prior to

TokenSwap

calling

transferFrom

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.13;

import "https://github.com/OpenZeppelin/openzeppelin-contracts/blob/v4.0.0/contracts/token/ERC20/IERC20.sol";

/*
How to swap tokens

1. Alice has 100 tokens from AliceCoin, which is a ERC20 token.
2. Bob has 100 tokens from BobCoin, which is also a ERC20 token.
3. Alice and Bob wants to trade 10 AliceCoin for 20 BobCoin.
4. Alice or Bob deploys TokenSwap
5. Alice approves TokenSwap to withdraw 10 tokens from AliceCoin
6. Bob approves TokenSwap to withdraw 20 tokens from BobCoin
7. Alice or Bob calls TokenSwap.swap()
8. Alice and Bob traded tokens successfully.
*/

contract TokenSwap {
    IERC20 public token1;
    address public owner1;
    uint public amount1;
    IERC20 public token2;
    address public owner2;
    uint public amount2;

    constructor(
        address _token1,
        address _owner1,
        uint _amount1,
        address _token2,
        address _owner2,
        uint _amount2
    ) {
        token1 = IERC20(_token1);
        owner1 = _owner1;
        amount1 = _amount1;
        token2 = IERC20(_token2);
        owner2 = _owner2;
        amount2 = _amount2;
    }

    function swap() public {
        require(msg.sender == owner1 || msg.sender == owner2, "Not authorized");
        require(
            token1.allowance(owner1, address(this)) >= amount1,
            "Token 1 allowance too low"
        );
        require(
            token2.allowance(owner2, address(this)) >= amount2,
            "Token 2 allowance too low"
        );

        _safeTransferFrom(token1, owner1, owner2, amount1);
        _safeTransferFrom(token2, owner2, owner1, amount2);
    }

    function _safeTransferFrom(
        IERC20 token,
        address sender,
        address recipient,
        uint amount
    ) private {
        bool sent = token.transferFrom(sender, recipient, amount);
        require(sent, "Token transfer failed");
    }
}