E0308 rust type_error ai_generated true

error[E0308]: `match` arms have incompatible types note: expected `Result<(), MyError>` found `Result<(), OtherError>`

ID: rust/e0308-match-arm-different-types-with-generic

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92%Fix Rate
83%Confidence
1Evidence
2023-10-05First Seen

Version Compatibility

VersionStatusIntroducedDeprecatedNotes
rustc 1.74 active — — —
rustc 1.75 active — — —

Root Cause

Different match arms return `Result` types with different error types, even if both implement `From` or `Into`.

generic

中文

不同的 match 分支返回具有不同错误类型的 `Result` 类型，即使两者都实现了 `From` 或 `Into`。

Official Documentation

https://doc.rust-lang.org/stable/error_codes/E0308.html

Workarounds

  1. 90% success Use `.map_err()` on each arm to convert errors to a common type: `arm1.map_err(|e| MyError::from(e))`. 
    Use `.map_err()` on each arm to convert errors to a common type: `arm1.map_err(|e| MyError::from(e))`.
  2. 95% success Define a unified error enum that wraps both error types and implement `From` for each. 
    Define a unified error enum that wraps both error types and implement `From` for each.

中文步骤

  1. 在每个分支上使用 `.map_err()` 将错误转换为公共类型：`arm1.map_err(|e| MyError::from(e))`。
  2. 定义一个统一的错误枚举，包装两种错误类型，并为每种类型实现 `From`。

Dead Ends

Common approaches that don't work:

  1. 70% fail

    Only fixes one arm; compiler still sees mismatch if the other arm has a different error type.

  2. 85% fail

    Panics on error; not a proper fix for error handling.