From 593f9293b9a9e3c7ddd2a230578a2284a9163ec4 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Linus=20F=C3=A4rnstrand?= <faern@faern.net>
Date: Tue, 23 Mar 2021 21:24:26 +0100
Subject: [PATCH 1/2] Add Result::into_err where the Ok variant can never
happen
---
library/core/src/result.rs | 36 ++++++++++++++++++++++++++++++++++++
1 file changed, 36 insertions(+)
diff --git a/library/core/src/result.rs b/library/core/src/result.rs
index 2ce8a703c123e..20f8095b7d1ce 100644
--- a/library/core/src/result.rs
+++ b/library/core/src/result.rs
@@ -1167,6 +1167,42 @@ impl<T, E: Into<!>> Result<T, E> {
}
}
+#[unstable(feature = "unwrap_infallible", reason = "newly added", issue = "61695")]
+impl<T: Into<!>, E> Result<T, E> {
+ /// Returns the contained [`Err`] value, but never panics.
+ ///
+ /// Unlike [`unwrap_err`], this method is known to never panic on the
+ /// result types it is implemented for. Therefore, it can be used
+ /// instead of `unwrap_err` as a maintainability safeguard that will fail
+ /// to compile if the ok type of the `Result` is later changed
+ /// to a type that can actually occur.
+ ///
+ /// [`unwrap_err`]: Result::unwrap_err
+ ///
+ /// # Examples
+ ///
+ /// Basic usage:
+ ///
+ /// ```
+ /// # #![feature(never_type)]
+ /// # #![feature(unwrap_infallible)]
+ ///
+ /// fn only_bad_news() -> Result<!, String> {
+ /// Err("Oops, it failed".into())
+ /// }
+ ///
+ /// let error: String = only_bad_news().into_err();
+ /// println!("{}", error);
+ /// ```
+ #[inline]
+ pub fn into_err(self) -> E {
+ match self {
+ Ok(x) => x.into(),
+ Err(e) => e,
+ }
+ }
+}
+
impl<T: Deref, E> Result<T, E> {
/// Converts from `Result<T, E>` (or `&Result<T, E>`) to `Result<&<T as Deref>::Target, &E>`.
///
From 3bf076e76b2afde77f1c0d2c763cef32407f0465 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Linus=20F=C3=A4rnstrand?= <faern@faern.net>
Date: Tue, 23 Mar 2021 21:27:38 +0100
Subject: [PATCH 2/2] Add test for Result::into_err
---
library/core/tests/result.rs | 22 ++++++++++++++++++++++
1 file changed, 22 insertions(+)
diff --git a/library/core/tests/result.rs b/library/core/tests/result.rs
index 5fcd7b4d3a327..c461ab380ad3d 100644
--- a/library/core/tests/result.rs
+++ b/library/core/tests/result.rs
@@ -225,6 +225,28 @@ pub fn test_into_ok() {
assert_eq!(infallible_op2().into_ok(), 667);
}
+#[test]
+pub fn test_into_err() {
+ fn until_error_op() -> Result<!, isize> {
+ Err(666)
+ }
+
+ assert_eq!(until_error_op().into_err(), 666);
+
+ enum MyNeverToken {}
+ impl From<MyNeverToken> for ! {
+ fn from(never: MyNeverToken) -> ! {
+ match never {}
+ }
+ }
+
+ fn until_error_op2() -> Result<MyNeverToken, isize> {
+ Err(667)
+ }
+
+ assert_eq!(until_error_op2().into_err(), 667);
+}
+
#[test]
fn test_try() {
fn try_result_some() -> Option<u8> {