diff --git a/include/toolkit.h b/include/toolkit.h
index 828c724..8368625 100644
--- a/include/toolkit.h
+++ b/include/toolkit.h
@@ -29,8 +29,15 @@ concept _num_type = requires {
 
 namespace toolkit
 {
+    enum class num_type{
+      BIN,
+      HEX,
+      OCT,
+      DEC
+    }
+
     template <typename T>
-    std::expected<std::string, std::string> to_string(T value)
+    inline std::expected<std::string, std::string> to_string(T value)
     {
         if constexpr (std::is_same_v<T, int> || std::is_same_v<T, float> || std::is_same_v<T, double>)
         {
@@ -50,7 +57,7 @@ namespace toolkit
     }
 
     template <typename T = double> // requires std::is_same_v<T, std::string>
-    std::expected<T, std::string> stoi(const std::string &str)
+    inline std::expected<T, std::string> stoi(const std::string &str)
     {
         T value;
         auto res = std::from_chars(str.c_str(), str.c_str() + str.size(), value);
@@ -63,7 +70,7 @@ namespace toolkit
 
     template <typename T>
         requires std::is_same_v<std::string, T> || std::is_same_v<const char *, T>
-    std::string replace_string(const std::string &str, T d, T e)
+    inline std::string replace_string(const std::string &str, T d, T e)
     {
         std::string result = str;
         if (d == e)
@@ -93,7 +100,7 @@ namespace toolkit
     template <typename T = std::string>
         requires std::is_same_v<T, std::string> ||
                  std::is_same_v<T, std::string_view>
-    std::vector<T> split(T str, T d)
+    inline std::vector<T> split(T str, T d)
     {
         auto v = views::split(str, d) | views::transform([](auto word)
                                                          { return T(word.begin(), word.end()); });