如何构建/解构枚举的枚举?

Question

我在枚举枚举上匹配时遇到问题。结构类似于这样：

enum WebEvent {
PageLoad,
PageUnload,
KeyPress(char),
Paste(String),
Click { x: i64, y: i64 },
}
enum KeyEvent {
UpPressed,
DownPressed,
}
enum Event {
WebEvent,
KeyEvent,
}
fn inspect(event: Event) {
match event {
Event::WebEvent::PageLoad => println!("page loaded"),
Event::WebEvent::PageUnload => println!("page unloaded"),
Event::WebEvent::KeyPress(c) => println!("pressed '{}'.", c),
Event::WebEvent::Paste(s) => println!("pasted "{}".", s),
Event::WebEvent::Click { x, y } => {
println!("clicked at x={}, y={}.", x, y);
}
Event::KeyEvent => {
println!("got a key event");
}
}
}
fn main() {
let pressed = WebEvent::KeyPress('x');
inspect(pressed);
}

操场

这是我从编译器得到的错误：

error[E0433]: failed to resolve. Not a module `WebEvent`
--> src/main.rs:20:16
|
20 |         Event::WebEvent::PageLoad => println!("page loaded"),
|                ^^^^^^^^ Not a module `WebEvent`
error[E0433]: failed to resolve. Not a module `WebEvent`
--> src/main.rs:21:16
|
21 |         Event::WebEvent::PageUnload => println!("page unloaded"),
|                ^^^^^^^^ Not a module `WebEvent`
error[E0433]: failed to resolve. Not a module `WebEvent`
--> src/main.rs:22:16
|
22 |         Event::WebEvent::KeyPress(c) => println!("pressed '{}'.", c),
|                ^^^^^^^^ Not a module `WebEvent`
error[E0433]: failed to resolve. Not a module `WebEvent`
--> src/main.rs:23:16
|
23 |         Event::WebEvent::Paste(s) => println!("pasted "{}".", s),
|                ^^^^^^^^ Not a module `WebEvent`
error[E0433]: failed to resolve. Not a module `WebEvent`
--> src/main.rs:24:16
|
24 |         Event::WebEvent::Click { x, y } => {
|                ^^^^^^^^ Not a module `WebEvent`
error[E0308]: mismatched types
--> src/main.rs:35:13
|
35 |     inspect(pressed);
|             ^^^^^^^ expected enum `Event`, found enum `WebEvent`
|
= note: expected type `Event`
found type `WebEvent`

构建/解构枚举的正确方法是什么？有什么办法可以做到这一点吗？

Answer 1

你忘记了枚举变体不是类型 - 你需要引入包装器才能让枚举能够包含其他枚举：

enum Event {
WebEvent(WebEvent),
KeyEvent(KeyEvent)
}

其余的非常简单：

enum WebEvent {
PageLoad,
PageUnload,
KeyPress(char),
Paste(String),
Click { x: i64, y: i64 },
}
enum KeyEvent {
UpPressed,
DownPressed,
}
enum Event {
WebEvent(WebEvent),
KeyEvent(KeyEvent)
}
fn inspect(event: Event) {
if let Event::WebEvent(webevt) = event {
match webevt {
WebEvent::PageLoad => println!("page loaded"),
WebEvent::PageUnload => println!("page unloaded"),
WebEvent::KeyPress(c) => println!("pressed '{}'.", c),
WebEvent::Paste(s) => println!("pasted "{}".", s),
WebEvent::Click { x, y } => println!("clicked at x={}, y={}.", x, y)
}
} else {
println!("got a key event")
}
}
fn main() {
let pressed = Event::WebEvent(WebEvent::KeyPress('x')); // note the extra wrap here
inspect(pressed);
}