《纸上谈兵·solidity》第 6 课：Solidity 数据存储布局 —— memory、storage、calldata 傻傻分不清？

contract Example {
    uint[] public values; // 默认在 storage 中

    function update() public {
        values.push(1); // 直接修改 storage
    }
}

function modify(uint[] storage arr) internal {
    arr[0] = 42; // 直接修改原始数组
}

function copy(uint[] memory data) public pure returns (uint) {
    data[0] = 123; // 修改的是 memory 中的副本
    return data[0];
}

contract DataTest {
    uint[] public data;

    constructor() {
        data.push(1);
        data.push(2);
        data.push(3);
    }

    // 修改副本（不改变原始 storage）
    function updateMemory() public view returns (uint[] memory) {
        uint[] memory temp = data;
        temp[0] = 99;
        return temp; // 原始 data 不变
    }

    // 修改 storage 变量本身
    function updateStorage() public {
        uint[] storage temp = data;
        temp[0] = 88;
    }
}

contract StorageTest is Test {
    DataTest dt;

    function setUp() public {
        dt = new DataTest();
    }

    function testUpdateMemoryDoesNotAffectStorage() public {
        uint[] memory result = dt.updateMemory();
        assertEq(result[0], 99);                // 复制体被改
        assertEq(dt.data(0), 1);                // storage 未改
    }

    function testUpdateStorageAffectsState() public {
        dt.updateStorage();
        assertEq(dt.data(0), 88);               // 状态变量被改变
    }
}

function readOnly(uint[] calldata data) external pure returns (uint) {
    // 编译失败
    data[0] = 10;
    return data[0]; // 不能修改 data
}

function sum(uint[] calldata nums) external pure returns (uint) {
    return nums[0] + nums[1];
}

// 编译失败
function fail(uint[] calldata nums) external {
    nums[0] = 1; // 不能修改 calldata
}

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

contract DataLocation {
    uint[] public store;

    function storeToMemory() public view returns (uint[] memory) {
        uint[] memory temp = new uint[](store.length);
        for (uint i = 0; i < store.length; i++) {
            temp[i] = store[i];
        }
        return temp;
    }

    function storeFromCalldata(uint[] calldata input) external {
        store = input; // 拷贝 calldata 到 storage
    }

    function getCalldata(uint[] calldata input) external pure returns (uint) {
        return input[0]; // 只能读，不能写
    }
}

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

import "forge-std/Test.sol";
import "../src/DataLocation.sol";

contract DataLocationTest is Test {
    DataLocation dl;

    function setUp() public {
        dl = new DataLocation();
    }

    function testMemoryCopy() public {
        uint[] memory input;
        input = new uint[](1);
        input[0] = 10;

        dl.storeFromCalldata(input);

        uint[] memory result = dl.storeToMemory();
        assertEq(result[0], 10);
    }

    function testGetCalldata() public view {
        uint[] memory arr;
        arr = new uint[](1);
        arr[0] = 42;

        uint val = dl.getCalldata(arr); 
        assertEq(val, 42);
    }
}

$ ➜  counter git:(main) ✗ forge test --match-path test/DataLocation.t.sol  -vvv
[⠊] Compiling...
[⠒] Compiling 1 files with Solc 0.8.30
[⠑] Solc 0.8.30 finished in 535.07ms
Compiler run successful!

Ran 2 tests for test/DataLocation.t.sol:DataLocationTest
[PASS] testGetCalldata() (gas: 10033)
[PASS] testMemoryCopy() (gas: 57458)
Suite result: ok. 2 passed; 0 failed; 0 skipped; finished in 4.60ms (2.16ms CPU time)

Ran 1 test suite in 182.96ms (4.60ms CPU time): 2 tests passed, 0 failed, 0 skipped (2 total tests)