rust/rust-error.md

@@ -266,4 +266,10 @@ fn main() -> Result<(), std::io::Error> {
     }
     Ok(())
 }
+```
+
+## 型変換
+### `Box<dyn std::error::Error>` to `anyhow::Error`
+``` rust
+box_error.map_err(|e| anyhow::anyhow!("{}", e))?;
 ```
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