rust/rust-error.md

+[[_TOC_]]
+
+### thiserror
+
+``` rs
+use std::fs::File;
+use thiserror::Error;
+
+#[derive(Error, Debug)]
+pub enum MyAppError {
+    #[error("Hoge error")]
+    Hoge,
+    #[error("IO error")]
+    IO(#[source] std::io::Error),
+}
+
+fn main() -> Result<(), MyAppError> {
+    let err = MyAppError::Hoge;
+    print!("err: {:?}\n", err);
+    let file_result = File::create(".").map_err(|e| MyAppError::IO(e));
+    print!("file_result: {:?}\n", file_result);
+    Ok(())
+}
+```
+
+``` bash
+err: Hoge
+file_result: Err(IO(Os { code: 21, kind: Other, message: "Is a directory" }))
+```
+
+`source`属性を付加すると既存のエラーをラップして独自のエラーの中に情報を追加できる
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