From c29e7ff9ac8478e78ba568d3d74a7a7c937456f9 Mon Sep 17 00:00:00 2001
From: Alex Shabalin <alex.shabalin@pm.me>
Date: Tue, 12 Mar 2024 11:21:38 +0100
Subject: [PATCH] Remove the is_constructible check because it breaks the
 usecase with forward declared types

---
 immer/box.hpp                   |  3 +--
 test/extra/archive/test_box.cpp | 18 ++++++++++++++++++
 2 files changed, 19 insertions(+), 2 deletions(-)

diff --git a/immer/box.hpp b/immer/box.hpp
index 711ac78f..ddf03636 100644
--- a/immer/box.hpp
+++ b/immer/box.hpp
@@ -74,8 +74,7 @@ class box
      */
     template <typename Arg,
               typename Enable = std::enable_if_t<
-                  !std::is_same<box, std::decay_t<Arg>>::value &&
-                  std::is_constructible<T, Arg>::value>>
+                  !std::is_same<box, std::decay_t<Arg>>::value>>
     box(Arg&& arg)
         : impl_{detail::make<heap, holder>(std::forward<Arg>(arg))}
     {}
diff --git a/test/extra/archive/test_box.cpp b/test/extra/archive/test_box.cpp
index 769a59b0..55dc0139 100644
--- a/test/extra/archive/test_box.cpp
+++ b/test/extra/archive/test_box.cpp
@@ -88,3 +88,21 @@ TEST_CASE("Test saving and mutating a box")
     const auto loaded2 = loader.load(id2);
     REQUIRE(loaded2.get() == "hello world");
 }
+
+namespace {
+struct fwd_type;
+struct test_type
+{
+    immer::box<fwd_type> data;
+};
+struct fwd_type
+{
+    int data = 123;
+};
+} // namespace
+
+TEST_CASE("Test box with a fwd declared type")
+{
+    auto val = test_type{};
+    REQUIRE(val.data.get().data == 123);
+}