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带标签的联合类型与 switch

对联合类型的各个变体进行模式匹配。

带标签的联合类型与 switch 是 CoddyKit 上的免费 Zig Academy 课时。这是第 3 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 Zig Academy 学习路径的一部分，你的进度在网页和 CoddyKit 应用中同步。 Zig Academy 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。

Remembering the Variant

A plain union forgets which field is active. A tagged union pairs the value with an enum tag that records the current variant.

Declaring a Tagged Union

You write union(enum) to let Zig generate a matching tag automatically, one tag name per field.

const Value = union(enum) { int: i64, text: []const u8 };

The Tag Tracks the Field

Now the value carries its own tag, like .int or .text. The union always knows which variant it currently holds.

var v = Value{ .int = 7 };

Switch over the Variants

Use switch on a tagged union to branch by variant. Each case names one tag and handles that shape of the value.

switch (v) { .int => {}, .text => {} }

Capture the Payload

Add a capture with vertical bars to pull out the inner value of the active field, ready to use inside that branch.

switch (v) { .int => |n| useInt(n), .text => |s| useText(s) }

Exhaustiveness Is Enforced

Zig requires every variant to be handled. Forget a case and the compiler stops you, so you never silently miss one.

The else Branch

When you want to handle the rest in one place, add an else branch to cover any variants you did not list explicitly.

switch (v) { .int => |n| useInt(n), else => {} }

switch Is an Expression

A switch can produce a value, so each branch returns something. You assign the whole switch to a variable in one step.

const kind = switch (v) { .int => 1, .text => 2 };

Mutate Through a Capture

Capture by pointer with |*field| when you want to change the payload in place rather than copy it out of the union.

switch (v) { .int => |*n| n.* += 1, else => {} }

A Type-Safe Sum Type

Tagged unions are Zig's safe sum types: one value, many shapes, and a switch that the compiler proves you handled completely.

Perfect for Parsers and States

This pattern fits tokens, AST nodes, and state machines beautifully: model each case once and let switch route the logic.

Quick Check

What does writing union(enum) give you over a plain union?

Recap

You met tagged unions: union(enum) tracks the active variant. Switch over it, capture payloads with bars, and the compiler enforces every case. 🧩

常见问题解答

「带标签的联合类型与 switch」课时是免费的吗？

是的 — 「带标签的联合类型与 switch」的完整文本可在网页上免费阅读。要进行交互式练习（内置代码编辑器和全天候 AI 导师）并解锁 Zig Academy 课程的其余内容，请升级到 CoddyKit PRO。 Zig Academy 课程共包含 4 节课。

「带标签的联合类型与 switch」这节课中我会学到什么？

对联合类型的各个变体进行模式匹配。你通过在浏览器中直接运行的动手代码来练习 Zig Academy，全天候 AI 导师会在你学习这节课的过程中回答你的问题。

学习 Zig Academy 需要有经验吗？

无需任何先前经验。CoddyKit 上的 Zig Academy 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 3 节课，共 4 节。

「带标签的联合类型与 switch」课时需要多长时间？

大多数 CoddyKit 课程大约需要 5–10 分钟。每节课都很精短且互动，所以你能稳步进步，并在网页和应用中从离开的地方继续。

我能在这节 Zig Academy 课中编写并运行代码吗？

能。每节 Zig Academy 课都包含内置代码编辑器，你可以在浏览器中直接编写并运行真实代码，并获得即时 AI 反馈 — 无需本地设置。

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