From a18e18394df62350eb9914fae7af2ea885189165 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Felix=20G=C3=BCndling?= <felix.guendling@gmail.com>
Date: Thu, 4 Apr 2024 17:31:58 +0200
Subject: [PATCH] variant: support std::visit via apply

---
 include/cista/containers/variant.h |  5 +++++
 test/variant_test.cc               | 12 ++++++++++++
 2 files changed, 17 insertions(+)

diff --git a/include/cista/containers/variant.h b/include/cista/containers/variant.h
index 9c4c2a4b..57b13020 100755
--- a/include/cista/containers/variant.h
+++ b/include/cista/containers/variant.h
@@ -438,6 +438,11 @@ using cista::variant;
 
 namespace std {
 
+template <typename Visitor, typename... T>
+constexpr auto visit(Visitor&& vis, cista::variant<T...>&& v) {
+  v.apply(vis);
+}
+
 using cista::get;
 
 }  // namespace std
diff --git a/test/variant_test.cc b/test/variant_test.cc
index 631a54e9..570503b9 100755
--- a/test/variant_test.cc
+++ b/test/variant_test.cc
@@ -241,3 +241,15 @@ TEST_CASE("variant get_if") {
   REQUIRE(str != nullptr);
   CHECK(*str == "hello test test test test");
 }
+
+TEST_CASE("std visit") {
+  std::visit(
+      [](auto&& x) {
+        if constexpr (std::is_same_v<int, std::decay_t<decltype(x)>>) {
+          CHECK(true);
+        } else {
+          CHECK(false);
+        }
+      },
+      cista::variant<int, float>{1});
+}