add PtrSelector

common/ptr_selector.hh

@@ -0,0 +1,43 @@
+#pragma once
+
+#include <typeinfo>
+
+#include "nf7.hh"
+
+
+namespace nf7 {
+
+template <typename Base, typename... I>
+struct PtrSelector final {
+ public:
+  PtrSelector(const std::type_info& t) noexcept : type_(&t) { }
+  PtrSelector(const PtrSelector&) = delete;
+  PtrSelector(PtrSelector&&) = delete;
+  PtrSelector& operator=(const PtrSelector&) = delete;
+  PtrSelector& operator=(PtrSelector&&) = delete;
+
+  template <typename T1, typename... T2>
+  Base* Select(T1 ptr1, T2... ptr2) noexcept {
+    auto ptr = Get<T1, I...>(ptr1);
+    return ptr? ptr: Select(ptr2...);
+  }
+  Base* Select() noexcept { return nullptr; }
+
+ private:
+  template <typename T, typename I1, typename... I2>
+  Base* Get(T ptr) const noexcept {
+    if constexpr (std::is_base_of<I1, std::remove_pointer_t<T>>::value) {
+      if (*type_ == typeid(I1)) return static_cast<I1*>(ptr);
+    }
+    return Get<T, I2...>(ptr);
+  }
+  template <typename T>
+  Base* Get(T) const noexcept { return nullptr; }
+
+  const std::type_info* const type_;
+};
+
+template <typename... I>
+using InterfaceSelector = PtrSelector<File::Interface, I...>;
+
+}  // namespace nf7