use namespace & not fix return

engine.h

@@ -0,0 +1,54 @@
+#ifndef MRUBYPP_H
+#define MRUBYPP_H
+
+#include "arena_guard.h"
+#include "bind_class.h"
+#include "converters.h"
+
+#include <functional>
+#include <mruby.h>
+#include <string>
+
+#include <mruby/compile.h>
+
+namespace mrubypp {
+class engine {
+public:
+  engine() { mrb_ = mrb_open(); }
+  ~engine() { mrb_close(mrb_); }
+  void load(const std::string &str) {
+    if (!mrb_)
+      return;
+    mrb_load_string(mrb_, str.c_str());
+  }
+
+  template <typename T> T call(const std::string &funcName) {
+    arena_guard guard(mrb_);
+    mrb_value result =
+        mrb_funcall(mrb_, mrb_top_self(mrb_), funcName.data(), 0);
+    return converter<T>::from_mrb(mrb_, result);
+  }
+
+  template <typename T, typename... Args>
+  T call(const std::string &funcName, Args... args) {
+    arena_guard guard(mrb_);
+    mrb_value argv[] = {converter<Args>::to_mrb(mrb_, args)...};
+    mrb_sym sym = mrb_intern_cstr(mrb_, funcName.data());
+    mrb_value result =
+        mrb_funcall_argv(mrb_, mrb_top_self(mrb_), sym, sizeof...(Args), argv);
+    return converter<T>::from_mrb(mrb_, result);
+  }
+
+  template <typename T>
+  class_builder<T> class_builder(const std::string &class_name) {
+    return class_builder<T>(mrb_, class_name);
+  }
+
+  [[nodiscard]] mrb_state *get_mrb() const { return mrb_; }
+
+private:
+  mrb_state *mrb_;
+};
+} // namespace mrubypp
+
+#endif // MRUBYPP_H