Rollup merge of #40335 - tbu-:pr_doc_str_to_somecase, r=steveklabnik

Document why `str.to_{lower,upper}case` return `String` Fixes #39201.
rust-lang · Mar 8, 2017 · f2886e8 · f2886e8
2 parents aea8010 + f3a2f90
commit f2886e8
Showing 1 changed file with 8 additions and 0 deletions.
diff --git a/src/libcollections/str.rs b/src/libcollections/str.rs
@@ -1646,6 +1646,10 @@ impl str {
     /// 'Lowercase' is defined according to the terms of the Unicode Derived Core Property
     /// `Lowercase`.
     ///
+    /// Since some characters can expand into multiple characters when changing
+    /// the case, this function returns a [`String`] instead of modifying the
+    /// parameter in-place.
+    ///
     /// [`String`]: string/struct.String.html
     ///
     /// # Examples
@@ -1718,6 +1722,10 @@ impl str {
     /// 'Uppercase' is defined according to the terms of the Unicode Derived Core Property
     /// `Uppercase`.
     ///
+    /// Since some characters can expand into multiple characters when changing
+    /// the case, this function returns a [`String`] instead of modifying the
+    /// parameter in-place.
+    ///
     /// [`String`]: string/struct.String.html
     ///
     /// # Examples