0. 版本

[openzeppelin]：v4.8.3，[forge-std]：v1.5.6

0.1 ERC20Capped.sol

Github: https://github.com/OpenZeppelin/openzeppelin-contracts/blob/v4.8.3/contracts/token/ERC20/extensions/ERC20Capped.sol

ERC20Capped库是ERC20的拓展。该库设置了ERC20发行量的上限。

1. 目标合约

继承ERC20Capped合约：

Github: https://github.com/RevelationOfTuring/foundry-openzeppelin-contracts/blob/master/src/token/ERC20/extensions/MockERC20Capped.sol

// SPDX-License-Identifier: UNLICENSED
pragma solidity ^0.8.0;

import "openzeppelin-contracts/contracts/token/ERC20/extensions/ERC20Capped.sol";

contract MockERC20Capped is ERC20Capped {
    constructor(string memory name, string memory symbol, uint cap)
    ERC20(name, symbol)
    ERC20Capped(cap){}

    function mint(address account, uint amount) external {
        _mint(account, amount);
    }
}

全部foundry测试合约：

Github: https://github.com/RevelationOfTuring/foundry-openzeppelin-contracts/blob/master/test/token/ERC20/extensions/ERC20Capped.t.sol

2. 代码精读

2.1 constructor() && cap()

• constructor()：初始化函数对发行量上限进行了设置；
• cap()：返回ERC20发行量上限

	// token发行量上限（immutable类型，合约初始化后无法再更改）
    uint256 private immutable _cap;

    constructor(uint256 cap_) {
    	// 要求设置的发行量上限大于0
        require(cap_ > 0, "ERC20Capped: cap is 0");
        // 设置上限
        _cap = cap_;
    }

    function cap() public view virtual returns (uint256) {
        // 返回常量_cap的值
        return _cap;
    }

foundry代码验证：

contract ERC20CappedTest is Test {
    MockERC20Capped private _testing = new MockERC20Capped("test name", "test symbol", 100);

    function test_Constructor() external {
        assertEq(_testing.cap(), 100);

        // revert with 0 cap in constructor
        vm.expectRevert("ERC20Capped: cap is 0");
        new MockERC20Capped("test name", "test symbol", 0);
    }
}

2.2 _mint(address account, uint256 amount)

为account地址铸造数量为amount的token。

    function _mint(address account, uint256 amount) internal virtual override {
        // 检查本次mint后的总发行量不得大于发行量上限
        require(ERC20.totalSupply() + amount <= cap(), "ERC20Capped: cap exceeded");
        // 调用ERC20.mint()进行铸造
        super._mint(account, amount);
    }

foundry代码验证：

contract ERC20CappedTest is Test {
    MockERC20Capped private _testing = new MockERC20Capped("test name", "test symbol", 100);
    address private user = address(1);

    function test_Mint() external {
        _testing.mint(user, 100);
        assertEq(_testing.totalSupply(), 100);

        vm.expectRevert("ERC20Capped: cap exceeded");
        _testing.mint(user, 1);
    }
}

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