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+---
+title: Rust 闭包 lifetime may not live long enough 问题
+date: 2023-05-24 18:04:23
+tags: [Technique]
+---
+
+代码：
+```rust
+...
+    fn handlers(self) -> crate::server::request::Handlers {
+        vec![(
+            "/tree",
+            routing::get(move || async {
+                (
+                    StatusCode::OK,
+                    Json(json!(self.clone().tree(self.clone().root))),
+                )
+            }),
+        )]
+    }
+...
+```
+
+编译错误：
+```text
+error: lifetime may not live long enough
+  --> src/storage/filesystem/mod.rs:45:34
+   |
+45 |               routing::get(move || async {
+   |  __________________________-------_^
+   | |                          |     |
+   | |                          |     return type of closure `{async block@src/storage/filesystem/mod.rs:45:34: 50:14}` contains a lifetime `'2`
+   | |                          lifetime `'1` represents this closure's body
+46 | |                 (
+47 | |                     StatusCode::OK,
+48 | |                     Json(json!(self.clone().tree(self.clone().root))),
+49 | |                 )
+50 | |             }),
+   | |_____________^ returning this value requires that `'1` must outlive `'2`
+   |
+   = note: closure implements `Fn`, so references to captured variables can't escape the closure
+```
+
+这是因为 `handlers` 里面的闭包捕获了一个引用，并且尝试返回一个包含该引用的值导致的。
+
+细说就是：闭包内部使用了 `self.clone()` 来获取一个新的实例，然后在异步块中返回一个 JSON 对象，这个 JSON 对象依赖于 `self.tree()` 的结果。因为闭包捕获了 `self` 的引用，所以它必须保证 `self` 在闭包执行完毕后仍然有效。
+
+解决这个问题的思路是：确保闭包中的所有引用都在闭包执行完毕之前就不再被使用。
+就是说，要将闭包的作用域限制在一个更短的生命周期内，或者使用其他方式来避免闭包捕获长期存在的引用:
+
+```rust
+
+...
+    fn handlers(self) -> crate::server::request::Handlers {
+        let tree = json!(self.clone().tree(self.clone().root));
+        vec![(
+            "/tree",
+            routing::get(move || async { (StatusCode::OK, Json(tree)) }),
+        )]
+    }
+...
+```
+\ No newline at end of file