From a1f3114ccc1e90b4748ec2b9e1eb9ddc3e3a325c Mon Sep 17 00:00:00 2001
From: Klas Marcks <klas.marcks@gmail.com>
Date: Sat, 17 Feb 2024 18:11:45 +0100
Subject: [PATCH] Use concepts instead of std::void_t when detecting to_child
 functions.

---
 CMakeLists.txt                           |  2 +-
 TSConfigVersion.cmake                    | 48 +++++++++++++++++++++---
 include/ts/typesafe_coordinate_systems.h | 30 ++++-----------
 3 files changed, 50 insertions(+), 30 deletions(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 534764d..dbf40dd 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -2,7 +2,7 @@ cmake_minimum_required(VERSION 3.18 FATAL_ERROR)
 
 set(CMAKE_CXX_STANDARD 20)
 
-project(TS VERSION 0.2.0 LANGUAGES CXX)
+project(TS VERSION 0.2.1 LANGUAGES CXX)
 
 enable_testing()
 
diff --git a/TSConfigVersion.cmake b/TSConfigVersion.cmake
index a0d2d7b..684e1ab 100644
--- a/TSConfigVersion.cmake
+++ b/TSConfigVersion.cmake
@@ -9,16 +9,52 @@
 # The variable CVF_VERSION must be set before calling configure_file().
 
 
-set(PACKAGE_VERSION "0.2.0")
+if (PACKAGE_FIND_VERSION_RANGE)
+  message(AUTHOR_WARNING
+    "`find_package()` specify a version range but the version strategy "
+    "(ExactVersion) of the module `${PACKAGE_FIND_NAME}` is incompatible "
+    "with this request. Only the lower endpoint of the range will be used.")
+endif()
+
+set(PACKAGE_VERSION "0.2.1")
+
+if("0.2.1" MATCHES "^([0-9]+)\\.([0-9]+)\\.([0-9]+)") # strip the tweak version
+  set(CVF_VERSION_MAJOR "${CMAKE_MATCH_1}")
+  set(CVF_VERSION_MINOR "${CMAKE_MATCH_2}")
+  set(CVF_VERSION_PATCH "${CMAKE_MATCH_3}")
 
-if("0.2.0" MATCHES "^([0-9]+\\.[0-9]+\\.[0-9]+)\\.") # strip the tweak version
-  set(CVF_VERSION_NO_TWEAK "${CMAKE_MATCH_1}")
+  if(NOT CVF_VERSION_MAJOR VERSION_EQUAL 0)
+    string(REGEX REPLACE "^0+" "" CVF_VERSION_MAJOR "${CVF_VERSION_MAJOR}")
+  endif()
+  if(NOT CVF_VERSION_MINOR VERSION_EQUAL 0)
+    string(REGEX REPLACE "^0+" "" CVF_VERSION_MINOR "${CVF_VERSION_MINOR}")
+  endif()
+  if(NOT CVF_VERSION_PATCH VERSION_EQUAL 0)
+    string(REGEX REPLACE "^0+" "" CVF_VERSION_PATCH "${CVF_VERSION_PATCH}")
+  endif()
+
+  set(CVF_VERSION_NO_TWEAK "${CVF_VERSION_MAJOR}.${CVF_VERSION_MINOR}.${CVF_VERSION_PATCH}")
 else()
-  set(CVF_VERSION_NO_TWEAK "0.2.0")
+  set(CVF_VERSION_NO_TWEAK "0.2.1")
 endif()
 
-if(PACKAGE_FIND_VERSION MATCHES "^([0-9]+\\.[0-9]+\\.[0-9]+)\\.") # strip the tweak version
-  set(REQUESTED_VERSION_NO_TWEAK "${CMAKE_MATCH_1}")
+if(PACKAGE_FIND_VERSION MATCHES "^([0-9]+)\\.([0-9]+)\\.([0-9]+)") # strip the tweak version
+  set(REQUESTED_VERSION_MAJOR "${CMAKE_MATCH_1}")
+  set(REQUESTED_VERSION_MINOR "${CMAKE_MATCH_2}")
+  set(REQUESTED_VERSION_PATCH "${CMAKE_MATCH_3}")
+
+  if(NOT REQUESTED_VERSION_MAJOR VERSION_EQUAL 0)
+    string(REGEX REPLACE "^0+" "" REQUESTED_VERSION_MAJOR "${REQUESTED_VERSION_MAJOR}")
+  endif()
+  if(NOT REQUESTED_VERSION_MINOR VERSION_EQUAL 0)
+    string(REGEX REPLACE "^0+" "" REQUESTED_VERSION_MINOR "${REQUESTED_VERSION_MINOR}")
+  endif()
+  if(NOT REQUESTED_VERSION_PATCH VERSION_EQUAL 0)
+    string(REGEX REPLACE "^0+" "" REQUESTED_VERSION_PATCH "${REQUESTED_VERSION_PATCH}")
+  endif()
+
+  set(REQUESTED_VERSION_NO_TWEAK
+      "${REQUESTED_VERSION_MAJOR}.${REQUESTED_VERSION_MINOR}.${REQUESTED_VERSION_PATCH}")
 else()
   set(REQUESTED_VERSION_NO_TWEAK "${PACKAGE_FIND_VERSION}")
 endif()
diff --git a/include/ts/typesafe_coordinate_systems.h b/include/ts/typesafe_coordinate_systems.h
index a8956ff..2be79fa 100644
--- a/include/ts/typesafe_coordinate_systems.h
+++ b/include/ts/typesafe_coordinate_systems.h
@@ -1,6 +1,7 @@
 #pragma once
 
 #include <type_traits>
+#include <concepts>
 
 // This file implements type-safe coordinate transformations.
 //
@@ -91,34 +92,17 @@
 //    This is more complicated than finding all 'to_parent' functions as under 1. This is because
 //    the parent systems are not aware of their children.
 //    This a recursive procedure and the responsible function is 'down'.
-//    To detect existing to_child functions we use SFINAE (Substitution Failure Is Not An Error).
-//    The responsible functions are the overoaded find_function::to_child functions.
+//    To detect existing to_child functions we use 'concepts'
 
 namespace ts{
 namespace find_function {
 
-// Compile time check if a to_child function with specific arguments exists.
-namespace internal {
+template <typename... Args>
+concept to_child = requires(Args ... args)
+{
+    transform::to_child(args...);
+};
 
-// Define template variable to_child that defaults to false.
-template <typename, typename, typename = void, typename...>
-constexpr bool to_child = false;
-
-// Specialization of templateVariable to_child.
-// The template argument std::void_t<decltype(transform::to_child(std::declval<Arg1>(), std::declval<Arg2>(), std::declval<GeometryState>()...))>
-// has the 'type' ´void´ if the decltype expression is valid after substitution.
-template <typename Arg1, typename Arg2, typename... GeometryState>
-constexpr bool to_child<Arg1,
-                       Arg2,
-                       std::void_t<decltype(transform::to_child(std::declval<Arg1>(), std::declval<Arg2>(), std::declval<GeometryState>()...))>,
-                       GeometryState...> = true;
-} // namespace internal
-
-// Interface variable to internal::to_child.
-// template arguments, Arg1, Arg2, void, GeometryState..., will match the specialization above if the decltype expression can be evaluated and
-// find_function::to_child will evaluate to true. Else find_function::to_child will be false.
-template <typename Arg1, typename Arg2, typename... GeometryState>
-constexpr bool to_child = internal::to_child<Arg1, Arg2, void, GeometryState...>;
 } // namespace find_function
 
 // Compile time detection of the common ancestor type of S1 and S2.