Add postgresql support

src/utils/is_one_of.hpp

@@ -0,0 +1,17 @@
+#pragma once
+
+#include <type_traits>
+
+template <typename...>
+struct is_one_of_implem {
+    static constexpr bool value = false;
+};
+
+template <typename F, typename S, typename... T>
+struct is_one_of_implem<F, S, T...> {
+    static constexpr bool value =
+        std::is_same<F, S>::value || is_one_of_implem<F, T...>::value;
+};
+
+template<typename... T>
+constexpr bool is_one_of = is_one_of_implem<T...>::value;

src/utils/optional_bool.cpp

@@ -0,0 +1,8 @@
+#include <utils/optional_bool.hpp>
+
+
+std::ostream& operator<<(std::ostream& os, const OptionalBool& o)
+{
+  os << o.to_string();
+  return os;
+}

src/utils/optional_bool.hpp

@@ -20,7 +20,7 @@ struct OptionalBool
     this->is_set = false;
   }
 
-  std::string to_string()
+  std::string to_string() const
   {
     if (this->is_set == false)
       return "unset";
@@ -33,3 +33,5 @@ struct OptionalBool
   bool is_set{false};
   bool value{false};
 };
+
+std::ostream& operator<<(std::ostream& os, const OptionalBool& o);