From ae4fe2bbc6dc2857785f7337d0351e4ee535be7f Mon Sep 17 00:00:00 2001
From: Eisenwave <me@eisenwave.net>
Date: Sun, 8 Mar 2026 21:14:55 +0100
Subject: [PATCH] Add summary and explanation of P1789

---
 .../expansion-statements-library-support.md   | 40 +++++++++++++++++++
 features_cpp26.yaml                           |  2 +
 2 files changed, 42 insertions(+)
 create mode 100644 content/expansion-statements-library-support.md

diff --git a/content/expansion-statements-library-support.md b/content/expansion-statements-library-support.md
new file mode 100644
index 0000000..b9233b1
--- /dev/null
+++ b/content/expansion-statements-library-support.md
@@ -0,0 +1,40 @@
+---
+execute: true
+---
+
+## What It Does
+
+`std::integer_sequence` can now be used in `template for`
+to conveniently write a loop where the loop index is a `constexpr` variable,
+as well as to create a `constexpr` pack using structured bindings.
+This is made possible by specializing `std::tuple_size`, `std::tuple_element`, and `std::get`
+for `std::integer_sequence`.
+
+## Why It Matters
+
+These changes remove boilerplate code such as creating an immediately invoked lambda expression
+when creating a `constexpr` pack of indices or writing a loop with a `constexpr` index.
+This is especially important because C++26 supports pack indexing,
+where a `constexpr` index is needed.
+
+## Example
+
+```cpp
+#include <utility>
+#include <tuple>
+#include <print>
+
+int main() {
+    auto tup = std::tuple{1, 3.14, "hello"};
+
+    // Output:
+    //   tup[0] = 1
+    //   tup[1] = 3.14
+    //   tup[2] = hello
+    template for (constexpr std::size_t I : std::make_index_sequence<3>()) {
+        std::println("tup[{}] = {}", I, std::get<I>(tup));
+    }
+
+    constexpr auto [...Is] = std::make_index_sequence<3>();
+}
+```
diff --git a/features_cpp26.yaml b/features_cpp26.yaml
index a358780..fc21536 100644
--- a/features_cpp26.yaml
+++ b/features_cpp26.yaml
@@ -1602,6 +1602,8 @@ features:
 
   - desc: "Library Support for Expansion Statements"
     paper: P1789
+    summary: "Specializes `std::tuple_size`, `std::tuple_element`, and `std::get` for `std::integer_sequence` to make it usable in expansion statements and structured bindings."
+    content: expansion-statements-library-support.md
     lib: true
     support: [Clang 22]
     ftm: