add singleton template

bin/utils/main.cpp

@@ -2,6 +2,7 @@
 
 #include "hack/logger/logger.hpp"
 #include "hack/utils/utils.hpp"
+#include "hack/utils/singleton.hpp"
 #include "hack/utils/func_query.hpp"
 
 int f(int a)
@@ -32,6 +33,14 @@ struct counter_test_2
   int id;
 };
 
+struct test_singleton : public hack::utils::singleton<test_singleton>
+{
+  void print()
+  {
+    hack::log()("Print singleton");
+  }
+};
+
 auto main(int argc, char *argv[]) -> int
 {
   {// ex: utils::func_memory
@@ -83,6 +92,10 @@ auto main(int argc, char *argv[]) -> int
     query = hack::utils::make_query("super_function");
     hack::log()("query", query);
   }
+
+  {// ex: singleton
+    test_singleton::get_instance().print();
+  }
 }