From bfd668cff2ad55e4da259ada2b09b1feabdae8ff Mon Sep 17 00:00:00 2001
From: "Timur A. Fatkhullin" <timur@sao.ru>
Date: Sat, 31 Jan 2026 13:03:48 +0300
Subject: [PATCH] ...

---
 mcc_serializer.h | 24 ++++++++++++++++++------
 1 file changed, 18 insertions(+), 6 deletions(-)

diff --git a/mcc_serializer.h b/mcc_serializer.h
index 5f2fc8b..a84dff9 100644
--- a/mcc_serializer.h
+++ b/mcc_serializer.h
@@ -12,10 +12,14 @@ namespace mcc
 struct mcc_serializer_interface_t {
     virtual ~mcc_serializer_interface_t() = default;
 
-    template <std::derived_from<mcc_serializer_interface_t> SelfT, traits::mcc_output_char_range R, typename ValueT>
-    mcc_error_c auto operator()(this SelfT&& self, R& output, ValueT&& value)
+    template <std::derived_from<mcc_serializer_interface_t> SelfT,
+              traits::mcc_output_char_range R,
+              typename ValueT,
+              typename FmtT = std::format_string<ValueT>>
+        requires(std::same_as<FmtT, std::format_string<ValueT>> || std::same_as<FmtT, std::string_view>)
+    mcc_error_c auto operator()(this SelfT&& self, R& output, ValueT&& value, FmtT fmt = "{}")
     {
-        return std::forward<SelfT>(self).operator=(output, std::forward<ValueT>(value));
+        return std::forward<SelfT>(self).operator=(output, std::forward<ValueT>(value), std::move(fmt));
     }
 };
 
@@ -23,6 +27,10 @@ template <typename T>
 concept mcc_serializer_c = std::derived_from<T, mcc_serializer_interface_t>;
 
 
+
+template <typename VT>
+class MccSerializer;
+
 template <typename VT>
 class MccSerializer : public mcc_serializer_interface_t
 {
@@ -35,10 +43,15 @@ public:
 
     ~MccSerializer() = default;
 
-    error_t operator()(traits::mcc_output_char_range auto& output, VT&& value)
+    template <typename FmtT = std::format_string<VT>>
+    error_t operator()(traits::mcc_output_char_range auto& output, VT&& value, FmtT fmt = "{}")
         requires std::formattable<VT, char>
     {
-        std::format_to(std::back_inserter(output), "{}", value);
+        if constexpr (std::same_as<FmtT, std::format_string<VT>>) {
+            std::format_to(std::back_inserter(output), fmt, value);
+        } else if constexpr (std::same_as<FmtT, std::string_view>) {
+            std::vformat_to(std::back_inserter(output), fmt, std::make_format_args(value));
+        }
 
         return {};
     }
@@ -48,7 +61,6 @@ protected:
 };
 
 
-
 template <mcc_angle_c T>
 class MccSerializer<T> : public mcc_serializer_interface_t
 {