Less unwrap() in documentation

Author: kornelski

library/alloc/src/collections/binary_heap/mod.rs

@@ -531,8 +531,7 @@ impl<T: Ord, A: Allocator> BinaryHeap<T, A> {
     /// heap.push(1);
     /// heap.push(5);
     /// heap.push(2);
-    /// {
-    ///     let mut val = heap.peek_mut().unwrap();
+    /// if let Some(mut val) = heap.peek_mut() {
     ///     *val = 0;
     /// }
     /// assert_eq!(heap.peek(), Some(&2));

library/core/src/cell/once.rs

@@ -262,7 +262,9 @@ impl<T> OnceCell<T> {
     ///
     /// let value = cell.get_mut_or_try_init(|| "1234".parse());
     /// assert_eq!(value, Ok(&mut 1234));
-    /// *value.unwrap() += 2;
+    ///
+    /// let Ok(value) = value else { return; };
+    /// *value += 2;
     /// assert_eq!(cell.get(), Some(&1236))
     /// ```
     #[unstable(feature = "once_cell_get_mut", issue = "121641")]
@@ -304,8 +306,8 @@ impl<T> OnceCell<T> {
     /// assert_eq!(cell.into_inner(), None);
     ///
     /// let cell = OnceCell::new();
-    /// cell.set("hello".to_string()).unwrap();
-    /// assert_eq!(cell.into_inner(), Some("hello".to_string()));
+    /// let _ = cell.set("hello".to_owned());
+    /// assert_eq!(cell.into_inner(), Some("hello".to_owned()));
     /// ```
     #[inline]
     #[stable(feature = "once_cell", since = "1.70.0")]
@@ -332,8 +334,8 @@ impl<T> OnceCell<T> {
     /// assert_eq!(cell.take(), None);
     ///
     /// let mut cell = OnceCell::new();
-    /// cell.set("hello".to_string()).unwrap();
-    /// assert_eq!(cell.take(), Some("hello".to_string()));
+    /// let _ = cell.set("hello".to_owned());
+    /// assert_eq!(cell.take(), Some("hello".to_owned()));
     /// assert_eq!(cell.get(), None);
     /// ```
     #[inline]

library/core/src/fmt/mod.rs

@@ -152,8 +152,9 @@ pub trait Write {
     /// }
     ///
     /// let mut buf = String::new();
-    /// writer(&mut buf, "hola").unwrap();
+    /// writer(&mut buf, "hola")?;
     /// assert_eq!(&buf, "hola");
+    /// # std::fmt::Result::Ok(())
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
     fn write_str(&mut self, s: &str) -> Result;
@@ -179,9 +180,10 @@ pub trait Write {
     /// }
     ///
     /// let mut buf = String::new();
-    /// writer(&mut buf, 'a').unwrap();
-    /// writer(&mut buf, 'b').unwrap();
+    /// writer(&mut buf, 'a')?;
+    /// writer(&mut buf, 'b')?;
     /// assert_eq!(&buf, "ab");
+    /// # std::fmt::Result::Ok(())
     /// ```
     #[stable(feature = "fmt_write_char", since = "1.1.0")]
     fn write_char(&mut self, c: char) -> Result {
@@ -208,8 +210,9 @@ pub trait Write {
     /// }
     ///
     /// let mut buf = String::new();
-    /// writer(&mut buf, "world").unwrap();
+    /// writer(&mut buf, "world")?;
     /// assert_eq!(&buf, "world");
+    /// # std::fmt::Result::Ok(())
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
     fn write_fmt(&mut self, args: Arguments<'_>) -> Result {

library/core/src/iter/sources/once.rs

@@ -34,7 +34,7 @@ use crate::iter::{FusedIterator, TrustedLen};
 /// use std::fs;
 /// use std::path::PathBuf;
 ///
-/// let dirs = fs::read_dir(".foo").unwrap();
+/// let dirs = fs::read_dir(".foo")?;
 ///
 /// // we need to convert from an iterator of DirEntry-s to an iterator of
 /// // PathBufs, so we use map
@@ -50,6 +50,7 @@ use crate::iter::{FusedIterator, TrustedLen};
 /// for f in files {
 ///     println!("{f:?}");
 /// }
+/// # std::io::Result::Ok(())
 /// ```
 #[stable(feature = "iter_once", since = "1.2.0")]
 pub fn once<T>(value: T) -> Once<T> {

library/core/src/iter/traits/iterator.rs

@@ -2564,7 +2564,7 @@ pub trait Iterator {
     /// # Example
     ///
     /// ```
-    /// let reduced: i32 = (1..10).reduce(|acc, e| acc + e).unwrap();
+    /// let reduced: i32 = (1..10).reduce(|acc, e| acc + e).unwrap_or(0);
     /// assert_eq!(reduced, 45);
     ///
     /// // Which is equivalent to doing it with `fold`:
@@ -3087,7 +3087,7 @@ pub trait Iterator {
     ///     [2.4, f32::NAN, 1.3]
     ///         .into_iter()
     ///         .reduce(f32::max)
-    ///         .unwrap(),
+    ///         .unwrap_or(0.),
     ///     2.4
     /// );
     /// ```
@@ -3123,7 +3123,7 @@ pub trait Iterator {
     ///     [2.4, f32::NAN, 1.3]
     ///         .into_iter()
     ///         .reduce(f32::min)
-    ///         .unwrap(),
+    ///         .unwrap_or(0.),
     ///     1.3
     /// );
     /// ```

library/core/src/option.rs

@@ -937,10 +937,16 @@ impl<T> Option<T> {
     /// Returns the contained [`Some`] value, consuming the `self` value.
     ///
     /// Because this function may panic, its use is generally discouraged.
+    /// Panics are meant for unrecoverable errors, and
+    /// [may abort the entire program][panic-abort].
+    ///
     /// Instead, prefer to use pattern matching and handle the [`None`]
     /// case explicitly, or call [`unwrap_or`], [`unwrap_or_else`], or
-    /// [`unwrap_or_default`].
+    /// [`unwrap_or_default`]. In functions returning `Option`, you can use
+    /// [the `?` (try) operator][try-option].
     ///
+    /// [panic-abort]: https://doc.rust-lang.org/book/ch09-01-unrecoverable-errors-with-panic.html
+    /// [try-option]: https://doc.rust-lang.org/book/ch09-02-recoverable-errors-with-result.html#where-the--operator-can-be-used
     /// [`unwrap_or`]: Option::unwrap_or
     /// [`unwrap_or_else`]: Option::unwrap_or_else
     /// [`unwrap_or_default`]: Option::unwrap_or_default

library/core/src/ptr/const_ptr.rs

@@ -502,11 +502,12 @@ impl<T: ?Sized> *const T {
     /// let mut out = String::new();
     /// while ptr != end_rounded_up {
     ///     unsafe {
-    ///         write!(&mut out, "{}, ", *ptr).unwrap();
+    ///         write!(&mut out, "{}, ", *ptr)?;
     ///     }
     ///     ptr = ptr.wrapping_offset(step);
     /// }
     /// assert_eq!(out.as_str(), "1, 3, 5, ");
+    /// # std::fmt::Result::Ok(())
     /// ```
     #[stable(feature = "ptr_wrapping_offset", since = "1.16.0")]
     #[must_use = "returns a new pointer rather than modifying its argument"]
@@ -1125,11 +1126,12 @@ impl<T: ?Sized> *const T {
     /// let mut out = String::new();
     /// while ptr != end_rounded_up {
     ///     unsafe {
-    ///         write!(&mut out, "{}, ", *ptr).unwrap();
+    ///         write!(&mut out, "{}, ", *ptr)?;
     ///     }
     ///     ptr = ptr.wrapping_add(step);
     /// }
     /// assert_eq!(out, "1, 3, 5, ");
+    /// # std::fmt::Result::Ok(())
     /// ```
     #[stable(feature = "pointer_methods", since = "1.26.0")]
     #[must_use = "returns a new pointer rather than modifying its argument"]
@@ -1203,11 +1205,12 @@ impl<T: ?Sized> *const T {
     /// let mut out = String::new();
     /// while ptr != start_rounded_down {
     ///     unsafe {
-    ///         write!(&mut out, "{}, ", *ptr).unwrap();
+    ///         write!(&mut out, "{}, ", *ptr)?;
     ///     }
     ///     ptr = ptr.wrapping_sub(step);
     /// }
     /// assert_eq!(out, "5, 3, 1, ");
+    /// # std::fmt::Result::Ok(())
     /// ```
     #[stable(feature = "pointer_methods", since = "1.26.0")]
     #[must_use = "returns a new pointer rather than modifying its argument"]

library/core/src/result.rs

@@ -1065,10 +1065,15 @@ impl<T, E> Result<T, E> {
     /// Returns the contained [`Ok`] value, consuming the `self` value.
     ///
     /// Because this function may panic, its use is generally discouraged.
-    /// Instead, prefer to use pattern matching and handle the [`Err`]
-    /// case explicitly, or call [`unwrap_or`], [`unwrap_or_else`], or
-    /// [`unwrap_or_default`].
+    /// Panics are meant for unrecoverable errors, and
+    /// [may abort the entire program][panic-abort].
+    ///
+    /// Instead, prefer to use [the `?` (try) operator][try-operator], or pattern matching
+    /// to handle the [`Err`] case explicitly, or call [`unwrap_or`],
+    /// [`unwrap_or_else`], or [`unwrap_or_default`].
     ///
+    /// [panic-abort]: https://doc.rust-lang.org/book/ch09-01-unrecoverable-errors-with-panic.html
+    /// [try-operator]: https://doc.rust-lang.org/book/ch09-02-recoverable-errors-with-result.html#a-shortcut-for-propagating-errors-the--operator
     /// [`unwrap_or`]: Result::unwrap_or
     /// [`unwrap_or_else`]: Result::unwrap_or_else
     /// [`unwrap_or_default`]: Result::unwrap_or_default

library/core/src/str/converts.rs

@@ -47,10 +47,11 @@ use crate::{mem, ptr};
 /// // some bytes, in a vector
 /// let sparkle_heart = vec![240, 159, 146, 150];
 ///
-/// // We know these bytes are valid, so just use `unwrap()`.
-/// let sparkle_heart = str::from_utf8(&sparkle_heart).unwrap();
+/// // We can use the ? (try) operator to check if the bytes are valid
+/// let sparkle_heart = str::from_utf8(&sparkle_heart)?;
 ///
 /// assert_eq!("💖", sparkle_heart);
+/// # Ok::<_, str::Utf8Error>(())
 /// ```
 ///
 /// Incorrect bytes:

library/core/src/sync/atomic.rs

@@ -86,7 +86,7 @@
 //!     // This is fine: `join` synchronizes the code in a way such that the atomic
 //!     // store happens-before the non-atomic write.
 //!     let handle = s.spawn(|| atomic.store(1, Ordering::Relaxed)); // atomic store
-//!     handle.join().unwrap(); // synchronize
+//!     handle.join().expect("thread won't panic"); // synchronize
 //!     s.spawn(|| unsafe { atomic.as_ptr().write(2) }); // non-atomic write
 //! });
 //!
@@ -103,7 +103,7 @@
 //!     // This is fine: `join` synchronizes the code in a way such that
 //!     // the 1-byte store happens-before the 2-byte store.
 //!     let handle = s.spawn(|| atomic.store(1, Ordering::Relaxed));
-//!     handle.join().unwrap();
+//!     handle.join().expect("thread won't panic");
 //!     s.spawn(|| unsafe {
 //!         let differently_sized = transmute::<&AtomicU16, &AtomicU8>(&atomic);
 //!         differently_sized.store(2, Ordering::Relaxed);