very, very simple WP with midi CC out

include/libremidi/detail/memory.hpp

@@ -0,0 +1,40 @@
+#pragma once
+
+#include <memory>
+#include <mutex>
+
+namespace libremidi
+{
+template <auto func>
+struct deleter
+{
+  template <typename U>
+  void operator()(U* x) noexcept(noexcept(func(x)))
+  {
+    func(x);
+  }
+};
+
+template <typename T, auto func>
+using unique_handle = std::unique_ptr<T, deleter<func>>;
+
+template <typename T>
+std::shared_ptr<T> instance()
+{
+  static std::mutex mut;
+  static std::weak_ptr<T> cache;
+
+  std::lock_guard _{mut};
+
+  if (auto ptr = cache.lock())
+  {
+    return ptr;
+  }
+  else
+  {
+    auto shared = std::make_shared<T>();
+    cache = shared;
+    return shared;
+  }
+}
+}