Web3 & DApp Development Fundamentals · 课时

引用类型

数组、结构体与映射

引用类型 是 CoddyKit 上的免费 Web3 & DApp Development Fundamentals 课时。这是第 2 节课，共 4 节。你可以在下方免费阅读本课时的完整内容 — 然后在浏览器中使用内置代码编辑器和全天候 AI 导师进行实践。这是 Web3 & DApp Development Fundamentals 学习路径的一部分，你的进度在网页和 CoddyKit 应用中同步。 Web3 & DApp Development Fundamentals 课程共包含 4 节课。

本课时的部分内容尚未翻译，以英文显示。

What Are Reference Types?

Reference types describe data that is too large to fit in one slot, so variables refer to a location rather than holding the data directly.

The three reference types are arrays, structs, and mappings. When you use them you must think about their data location: storage, memory, or calldata.

Fixed-Size Arrays

A fixed-size array has a length set at compile time and cannot grow. The type uint[3] always holds exactly three values.

Use .length to read the size. Out-of-bounds access reverts.

<code>uint[3] public scores = [10, 20, 30];

function first() public view returns (uint) {
    return scores[0];
}</code>

Dynamic Arrays

A dynamic array can grow and shrink. Declare it as uint[]. In storage you can push to append and pop to remove the last element.

<code>uint[] public nums;

function add(uint n) public {
    nums.push(n);
}

function removeLast() public {
    nums.pop();
}</code>

Bytes and String

bytes is a dynamically-sized byte array and string is its UTF-8 text cousin. Both are reference types.

Note: string has no .length or indexing; convert to bytes first to inspect raw bytes.

<code>string public name = 'Alice';

function nameLength() public view returns (uint) {
    return bytes(name).length;
}</code>

Defining Structs

A struct groups related variables into one custom type. It is ideal for modeling entities like users, orders, or tokens.

<code>struct User {
    string name;
    uint256 balance;
    bool active;
}</code>

Using Structs

You can create a struct with positional or named arguments and store it. Reading a struct from storage gives you a reference you can modify.

<code>User public owner;

function setup(string memory n) public {
    owner = User({ name: n, balance: 0, active: true });
}</code>

Mappings

A mapping is a key-value store, like a hash table. It is one of the most used structures in smart contracts, for example tracking balances per address.

Keys are not stored, so you cannot iterate a mapping or get its length.

<code>mapping(address => uint256) public balances;

function deposit() public payable {
    balances[msg.sender] += msg.value;
}</code>

Nested Mappings

Mappings can be nested to model relationships, such as allowances where one owner permits multiple spenders.

This pattern is the heart of the ERC-20 allowance system.

<code>mapping(address => mapping(address => uint256)) public allowance;

function approve(address spender, uint256 amount) public {
    allowance[msg.sender][spender] = amount;
}</code>

Combining Structs and Mappings

A powerful pattern is mapping keys to structs. This lets you store rich records keyed by an id or address.

<code>struct Order {
    uint256 amount;
    bool paid;
}

mapping(uint256 => Order) public orders;

function createOrder(uint256 id, uint256 amt) public {
    orders[id] = Order({ amount: amt, paid: false });
}</code>

Arrays of Structs

You can keep a dynamic array of structs when you need ordered, iterable records. Combine it with a mapping for fast lookup.

<code>struct Item { string name; uint256 price; }
Item[] public items;

function addItem(string memory n, uint256 p) public {
    items.push(Item(n, p));
}</code>

Reference Semantics

When you assign a storage reference type to a local storage variable, both point to the same data. Changes through one are visible through the other.

A memory copy, in contrast, is independent.

<code>uint[] public data;

function tweak() public {
    uint[] storage ref = data; // alias
    ref.push(42);              // also changes data
}</code>

Quick Check

Test your understanding of reference types.

Recap

You explored Solidity reference types:

Arrays (fixed and dynamic), plus bytes and string
Structs to group related fields
Mappings and nested mappings for key-value storage
Powerful combinations like mapping-to-struct and arrays-of-structs

Reference types share locations, so always be deliberate about storage versus memory.

常见问题解答

「引用类型」课时是免费的吗？

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无需任何先前经验。CoddyKit 上的 Web3 & DApp Development Fundamentals 课程适合初学者到高级学习者，你可以从这里开始或从头开始，按照自己的节奏学习。这是第 2 节课，共 4 节。

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