Add basic_cpp_entity_ref generalization

include/cppast/cpp_entity_ref.hpp

@@ -0,0 +1,52 @@
+// Copyright (C) 2017 Jonathan Müller <jonathanmueller.dev@gmail.com>
+// This file is subject to the license terms in the LICENSE file
+// found in the top-level directory of this distribution.
+
+#ifndef CPPAST_CPP_ENTITY_REF_HPP_INCLUDED
+#define CPPAST_CPP_ENTITY_REF_HPP_INCLUDED
+
+#include <cppast/cpp_entity_index.hpp>
+#include <cppast/cpp_entity_type.hpp>
+
+namespace cppast
+{
+    /// A basic reference to some kind of [cppast::cpp_entity]().
+    template <typename T, cpp_entity_type Type>
+    class basic_cpp_entity_ref
+    {
+    public:
+        /// \effects Creates it giving it the target id and name.
+        /// \requires An entity of matching type must eventually register in the [cppast::cpp_entity_index]() using that id.
+        basic_cpp_entity_ref(cpp_entity_id target_id, std::string target_name)
+        : target_(std::move(target_id)), name_(std::move(target_name))
+        {
+        }
+
+        /// \returns The name of the reference, as spelled in the source code.
+        const std::string& name() const noexcept
+        {
+            return name_;
+        }
+
+        /// \returns The [cppast::cpp_entity_id]() of the entity it refers to.
+        const cpp_entity_id& id() const noexcept
+        {
+            return target_;
+        }
+
+        /// \returns The [cppast::cpp_entity]() it refers to.
+        const T& get(const cpp_entity_index& idx) const noexcept
+        {
+            return detail::downcast_entity<const T&>(idx.lookup(target_).value(), Type);
+        }
+
+    private:
+        cpp_entity_id target_;
+        std::string   name_;
+    };
+
+    /// A [cppast::basic_cpp_entity_ref]() to any [cppast::cpp_entity]().
+    using cpp_entity_ref = basic_cpp_entity_ref<cpp_entity, cpp_entity_type::count>;
+} // namespace cppast
+
+#endif // CPPAST_CPP_ENTITY_REF_HPP_INCLUDED