22.Error

An error will undo all changes made to the state during a transaction.

You can throw an error by calling require, revert or assert.

• require is used to validate inputs and conditions before execution.
• revert is similar to require. See the code below for details.
• assert is used to check for code that should never be false. Failing assertion probably means that there is a bug.

Use custom error to save gas.

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.1;

contract ErrorIntro {
    function testRequire(uint256 _i) public pure {
        //         “Require” 应该用于验证以下条件：
        // 输入
        // 执行前的条件
        // 对其他函数调用的返回值
        require(_i > 10, "Input must be greater than 10");
    }

    function testRevert(uint256 _i) public pure {
        // 当需要检查的条件比较复杂时，Revert是非常有用的。 这段代码与上面的示例执行的是完全相同的操作。
        if (_i <= 10) {
            revert("Input must be greater than 10");
        }
    }

    uint256 public num;

    function testAssert() public view {
        //  Assert应该仅用于测试内部错误和检查不变量。
        assert(num == 0);
    }

    // 自定义error
    error MyError(address caller, uint256 i);

    function testCustomError(uint256 _i) public view {
        if (_i > 10) {
            revert MyError(msg.sender, _i);
        }
    }


}