From 318813def9fbc6ec75a4017d840e169a2bf5df0f Mon Sep 17 00:00:00 2001
From: mejrs <59372212+mejrs@users.noreply.github.com>
Date: Sat, 14 Oct 2023 23:41:00 +0200
Subject: [PATCH] Document `string_deref_patterns` feature

---
 .../string-deref-patterns.md                  | 45 +++++++++++++++++++
 1 file changed, 45 insertions(+)
 create mode 100644 src/doc/unstable-book/src/language-features/string-deref-patterns.md

diff --git a/src/doc/unstable-book/src/language-features/string-deref-patterns.md b/src/doc/unstable-book/src/language-features/string-deref-patterns.md
new file mode 100644
index 0000000000000..3723830751e80
--- /dev/null
+++ b/src/doc/unstable-book/src/language-features/string-deref-patterns.md
@@ -0,0 +1,45 @@
+# `string_deref_patterns`
+
+The tracking issue for this feature is: [#87121]
+
+[#87121]: https://github.com/rust-lang/rust/issues/87121
+
+------------------------
+
+This feature permits pattern matching `String` to `&str` through [its `Deref` implementation].
+
+```rust
+#![feature(string_deref_patterns)]
+
+pub enum Value {
+    String(String),
+    Number(u32),
+}
+
+pub fn is_it_the_answer(value: Value) -> bool {
+    match value {
+        Value::String("42") => true,
+        Value::Number(42) => true,
+        _ => false,
+    }
+}
+```
+
+Without this feature other constructs such as match guards have to be used.
+
+```rust
+# pub enum Value {
+#    String(String),
+#    Number(u32),
+# }
+#
+pub fn is_it_the_answer(value: Value) -> bool {
+    match value {
+        Value::String(s) if s == "42" => true,
+        Value::Number(42) => true,
+        _ => false,
+    }
+}
+```
+
+[its `Deref` implementation]: https://doc.rust-lang.org/std/string/struct.String.html#impl-Deref-for-String