From f75daa7c1a15330dde4225710d5d7810e8ce77ff Mon Sep 17 00:00:00 2001
From: Yaraslau Tamashevich <yaraslau.tamashevich@gmail.com>
Date: Thu, 11 Jul 2024 09:44:28 +0300
Subject: [PATCH] add same_as concept

---
 README.md           | 19 +++++++++++++++++++
 include/form/form.h |  5 ++++-
 src/main.cpp        |  1 +
 src/test.cpp        |  1 -
 src/test.h          | 20 ++++++++++++++++----
 5 files changed, 40 insertions(+), 6 deletions(-)

diff --git a/README.md b/README.md
index 5111e31..f839634 100644
--- a/README.md
+++ b/README.md
@@ -190,3 +190,22 @@ void runTests() { form::run_tests<^for_tests>(); }
 */
 
 ```
+
+## extension of same_as concept to templates
+
+concept `form::same_as` checks if type represent specific template 
+
+``` c++
+
+template <typename T> int foo(T) { return -1; }
+
+template <typename T>
+  requires form::same_as<T, ^std::complex>
+int foo(T) {
+  return 1;
+}
+
+
+foo(std::complex<float>{1,1}); //1
+
+```
diff --git a/include/form/form.h b/include/form/form.h
index f6561c7..9a9f2bb 100644
--- a/include/form/form.h
+++ b/include/form/form.h
@@ -107,7 +107,7 @@ template <typename S> consteval std::size_t get_padding() {
   std::size_t padding{0};
   std::size_t pointer{offset_of(nonstatic_data_members_of(^S)[0])};
 
-  [: util::expand(nonstatic_data_members_of(^S)):] >> [&, i = 0]<auto e>() {
+  [:util::expand(nonstatic_data_members_of(^S)):] >> [&, i = 0]<auto e>() {
     if (pointer == offset_of(e))
       pointer += size_of(e);
     else {
@@ -123,6 +123,9 @@ concept no_padding =
     std::same_as<std::integral_constant<std::size_t, get_padding<T>()>,
                  std::integral_constant<std::size_t, 0>>;
 
+template <typename T, auto refl>
+concept same_as = template_of(^T) == refl;
+
 } // namespace form
 
 template <> struct std::formatter<std::basic_string_view<char8_t>> {
diff --git a/src/main.cpp b/src/main.cpp
index 23e4c01..a5753af 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -1,5 +1,6 @@
 // SPDX-License-Identifier: Apache-2.0
 #include <boxed-cpp/boxed.hpp>
+#include <complex>
 #include <cstdio>
 #include <form/form.h>
 #include <print>
diff --git a/src/test.cpp b/src/test.cpp
index e3c75dc..1c932d0 100644
--- a/src/test.cpp
+++ b/src/test.cpp
@@ -2,6 +2,5 @@
 
 int main() {
   form::run_tests<^form::tests>();
-  form::run_tests<^form::round_trip_tests>();
   form::run_tests<^form::examples>();
 }
diff --git a/src/test.h b/src/test.h
index 1cf1552..bd55ae2 100644
--- a/src/test.h
+++ b/src/test.h
@@ -2,6 +2,7 @@
 #pragma once
 #include <algorithm>
 #include <boxed-cpp/boxed.hpp>
+#include <complex>
 #include <form/form.h>
 #include <print>
 #include <thread>
@@ -173,6 +174,18 @@ template <typename T> constexpr auto CreateClass() {
 // clang-format on
 
 } // namespace detail
+
+namespace form_same_as {
+template <typename T> int foo(T) { return -1; }
+
+template <typename T>
+  requires form::same_as<T, ^std::complex>
+int foo(T) {
+  return 1;
+}
+
+} // namespace form_same_as
+
 namespace form::tests {
 
 void testZ() {
@@ -230,9 +243,8 @@ void testSJson() {
   s.j = 2;
   std::println("{}", form::format_json(s));
 }
-} // namespace form::tests
 
-namespace form::round_trip_tests {
+bool CheckSameAs() { return form_same_as::foo(std::complex<float>{1, 1}) == 1; }
 
 bool compareTrue() {
   return form::compare(3.0, 3.0) && form::compare(3, 3) &&
@@ -312,7 +324,7 @@ bool ConfigRoundTrip() {
   return round_trip(config);
 }
 
-} // namespace form::round_trip_tests
+} // namespace form::tests
 
 namespace list {
 struct CancelSelection {};
@@ -349,8 +361,8 @@ template <form::no_padding T> void foo(T t) { std::println("Without padding"); }
 template <typename T> void foo(T t) {
   std::println("With padding: {}", form::get_padding<T>());
 }
-
 namespace form::examples {
+
 bool VariantCreate() {
   list_variant v{list::CancelSelection{}};
   return std::holds_alternative<list::CancelSelection>(v);