1 files changed, 39 insertions, 0 deletions
diff --git a/third_party/immer/extra/guile/scm/detail/invoke.hpp b/third_party/immer/extra/guile/scm/detail/invoke.hpp
new file mode 100644
index 000000000000..d9f2b37ccece
--- /dev/null
+++ b/third_party/immer/extra/guile/scm/detail/invoke.hpp
@@ -0,0 +1,39 @@
+//
+// immer: immutable data structures for C++
+// Copyright (C) 2016, 2017, 2018 Juan Pedro Bolivar Puente
+//
+// This software is distributed under the Boost Software License, Version 1.0.
+// See accompanying file LICENSE or copy at http://boost.org/LICENSE_1_0.txt
+//
+
+#pragma once
+
+// Adapted from the official std::invoke proposal:
+// http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2014/n4169.html
+
+#include <type_traits>
+#include <functional>
+
+namespace scm {
+namespace detail {
+
+template <typename Functor, typename... Args>
+std::enable_if_t<
+    std::is_member_pointer<std::decay_t<Functor>>::value,
+    std::result_of_t<Functor&&(Args&&...)>>
+invoke(Functor&& f, Args&&... args)
+{
+    return std::mem_fn(f)(std::forward<Args>(args)...);
+}
+
+template <typename Functor, typename... Args>
+std::enable_if_t<
+    !std::is_member_pointer<std::decay_t<Functor>>::value,
+    std::result_of_t<Functor&&(Args&&...)>>
+invoke(Functor&& f, Args&&... args)
+{
+    return std::forward<Functor>(f)(std::forward<Args>(args)...);
+}
+
+} // namespace detail
+} // namespace scm