Add a warning about Option/Result::and() being eagerly evaluated

Copied from `or()`.
rust-lang · Aug 23, 2022 · eb2fdd9 · eb2fdd9
1 parent ee8c31e
commit eb2fdd9
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Showing 2 changed files with 11 additions and 0 deletions.
diff --git a/library/core/src/option.rs b/library/core/src/option.rs
@@ -1189,6 +1189,12 @@ impl<T> Option<T> {
 
     /// Returns [`None`] if the option is [`None`], otherwise returns `optb`.
     ///
+    /// Arguments passed to `and` are eagerly evaluated; if you are passing the
+    /// result of a function call, it is recommended to use [`and_then`], which is
+    /// lazily evaluated.
+    ///
+    /// [`and_then`]: Option::and_then
+    ///
     /// # Examples
     ///
     /// ```

diff --git a/library/core/src/result.rs b/library/core/src/result.rs
@@ -1285,6 +1285,11 @@ impl<T, E> Result<T, E> {
 
     /// Returns `res` if the result is [`Ok`], otherwise returns the [`Err`] value of `self`.
     ///
+    /// Arguments passed to `and` are eagerly evaluated; if you are passing the
+    /// result of a function call, it is recommended to use [`and_then`], which is
+    /// lazily evaluated.
+    ///
+    /// [`and_then`]: Result::and_then
     ///
     /// # Examples
     ///