From b11f8ca9a379d3284a6bb8bf1ab690c3754d417b Mon Sep 17 00:00:00 2001
From: Asa Hammond <asa@automaton.is>
Date: Tue, 20 Feb 2024 19:45:11 -0800
Subject: [PATCH] constexpr only works on literal types

---
 test/util.cpp | 18 +++++++++++++++++-
 1 file changed, 17 insertions(+), 1 deletion(-)

diff --git a/test/util.cpp b/test/util.cpp
index baa68bb6..dbfca1fa 100644
--- a/test/util.cpp
+++ b/test/util.cpp
@@ -37,9 +37,25 @@ TEST_CASE("match deriv")
     CHECK(y == 42);
 }
 
+// only literal types can be used in a constexpr
+
+using literal_variant_t = std::variant<int, float, double>;
+struct literal_deriv_t : literal_variant_t
+{
+    using literal_variant_t::literal_variant_t;
+};
+
+TEST_CASE("match constexpr")
+{
+    constexpr auto v = literal_variant_t{42};
+    constexpr auto y =
+        lager::match(v)([](int x) { return x; }, [](auto) { return 0; });
+    CHECK(y == 42);
+}
+
 TEST_CASE("match deriv constexpr ")
 {
-    constexpr auto v = deriv_t{42};
+    constexpr auto v = literal_deriv_t{42};
     constexpr auto y =
         lager::match(v)([](int x) { return x; }, [](auto) { return 0; });
     CHECK(y == 42);