merge(3p/immer): Subtree merge at 'ad3e3556d' as 'third_party/immer'

Change-Id: I9636a41ad44b4218293833fd3e9456d9b07c731b

third_party/immer/test/vector/issue-74.cpp

@@ -0,0 +1,24 @@
+#include "immer/box.hpp"
+#include "immer/set.hpp"
+#include "immer/vector.hpp"
+
+#include <functional>
+
+struct my_type
+{
+    using container_t = immer::vector<immer::box<my_type>>;
+    using func_t      = std::function<int(int)>;
+
+    int ival;
+    double dval;
+    func_t func;
+    container_t children;
+};
+
+int main()
+{
+    my_type::container_t items = {my_type()};
+    immer::set<int> items2;
+    auto items3 = items2.insert(10);
+    return 0;
+}