From 37ebde53cfcf400ef01b59c80ae3f72039cd90f2 Mon Sep 17 00:00:00 2001
From: Abseil Team <absl-team@google.com>
Date: Mon, 1 Jul 2024 11:33:54 -0700
Subject: Make c_begin, c_end, and c_distance conditionally constexpr.

This allows them to be used in constexpr expressions, such as the following:

```
constexpr int distance = absl::c_distance(std::array<int, 3>());
```

Requires at least C++17 to be constexpr.

PiperOrigin-RevId: 648435141
Change-Id: I8136e351a6dc4c25f06ef895fb449f4f11048480
---
 absl/algorithm/container_test.cc | 11 +++++++++++
 1 file changed, 11 insertions(+)

(limited to 'absl/algorithm/container_test.cc')

diff --git a/absl/algorithm/container_test.cc b/absl/algorithm/container_test.cc
index 7e54e2b2..e5e2bf3d 100644
--- a/absl/algorithm/container_test.cc
+++ b/absl/algorithm/container_test.cc
@@ -15,6 +15,7 @@
 #include "absl/algorithm/container.h"
 
 #include <algorithm>
+#include <array>
 #include <functional>
 #include <initializer_list>
 #include <iterator>
@@ -31,6 +32,7 @@
 #include "gmock/gmock.h"
 #include "gtest/gtest.h"
 #include "absl/base/casts.h"
+#include "absl/base/config.h"
 #include "absl/base/macros.h"
 #include "absl/memory/memory.h"
 #include "absl/types/span.h"
@@ -1160,4 +1162,13 @@ TEST(MutatingTest, PermutationOperations) {
   EXPECT_EQ(initial, permuted);
 }
 
+#if defined(ABSL_INTERNAL_CPLUSPLUS_LANG) && \
+    ABSL_INTERNAL_CPLUSPLUS_LANG >= 201703L
+TEST(ConstexprTest, Distance) {
+  // Works at compile time with constexpr containers.
+  static_assert(absl::c_distance(std::array<int, 3>()) == 3);
+}
+#endif  // defined(ABSL_INTERNAL_CPLUSPLUS_LANG) &&
+        //  ABSL_INTERNAL_CPLUSPLUS_LANG >= 201703L
+
 }  // namespace
-- 
cgit v1.2.3