Require C++20 and update to C++20

.github/workflows/coverity.yml

@@ -13,7 +13,7 @@ jobs:
     - uses: cvmfs-contrib/github-action-cvmfs@v4
     - uses: aidasoft/run-lcg-view@v4
       with:
-        coverity-cmake-command: 'cmake -DCMAKE_CXX_STANDARD=17  -DENABLE_SIO=ON -DENABLE_JULIA=ON -DUSE_EXTERNAL_CATCH2=OFF ..'
+        coverity-cmake-command: 'cmake -DCMAKE_CXX_STANDARD=20  -DENABLE_SIO=ON -DENABLE_JULIA=ON -DUSE_EXTERNAL_CATCH2=OFF ..'
         coverity-project: 'AIDASoft%2Fpodio'
         coverity-project-token: ${{ secrets.PODIO_COVERITY_TOKEN }}
         github-pat: ${{ secrets.READ_COVERITY_IMAGE }}

.github/workflows/edm4hep.yaml

@@ -38,7 +38,7 @@ jobs:
             echo "::group::Build Catch2"
             cd $STARTDIR/catch2
             mkdir build && cd build
-            cmake -DCMAKE_CXX_STANDARD=17 -DCMAKE_INSTALL_PREFIX=../install -G Ninja ..
+            cmake -DCMAKE_CXX_STANDARD=20 -DCMAKE_INSTALL_PREFIX=../install -G Ninja ..
             ninja -k0 install
             export CMAKE_PREFIX_PATH=$STARTDIR/catch2/install:$CMAKE_PREFIX_PATH
             echo "::endgroup::"

.github/workflows/key4hep.yml

@@ -30,7 +30,7 @@ jobs:
           cmake -DENABLE_SIO=ON \
             -DENABLE_JULIA=OFF \
             -DCMAKE_INSTALL_PREFIX=../install \
-            -DCMAKE_CXX_STANDARD=17 \
+            -DCMAKE_CXX_STANDARD=20 \
             -DCMAKE_CXX_FLAGS=" -fdiagnostics-color=always -Werror -Wno-error=deprecated-declarations " \
             -DUSE_EXTERNAL_CATCH2=AUTO \
             -DENABLE_RNTUPLE=ON \

.github/workflows/ubuntu.yml

@@ -30,7 +30,7 @@ jobs:
             -DENABLE_JULIA=ON \
             -DENABLE_DATASOURCE=ON \
             -DCMAKE_INSTALL_PREFIX=../install \
-            -DCMAKE_CXX_STANDARD=17 \
+            -DCMAKE_CXX_STANDARD=20 \
             -DCMAKE_CXX_FLAGS=" -fdiagnostics-color=always -Werror -Wno-error=deprecated-declarations " \
             -DUSE_EXTERNAL_CATCH2=OFF \
             -DPODIO_SET_RPATH=ON \

CMakeLists.txt

@@ -34,9 +34,9 @@ endif()
 
 # Set up C++ Standard
 # ``-DCMAKE_CXX_STANDARD=<standard>`` when invoking CMake
-set(CMAKE_CXX_STANDARD 17 CACHE STRING "")
+set(CMAKE_CXX_STANDARD 20 CACHE STRING "")
 
-if(NOT CMAKE_CXX_STANDARD MATCHES "17|20")
+if(NOT CMAKE_CXX_STANDARD MATCHES "20|23")
   message(FATAL_ERROR "Unsupported C++ standard: ${CMAKE_CXX_STANDARD}")
 endif()
 
@@ -108,18 +108,13 @@ else()
   message(STATUS "Determined ROOT c++ standard: " ${ROOT_CXX_STANDARD})
 endif()
 
-if(ROOT_CXX_STANDARD VERSION_LESS 17)
-  message(FATAL_ERROR "You are trying to build podio against a version of ROOT that has not been built with a sufficient c++ standard. podio requires c++17 or higher")
+if(ROOT_CXX_STANDARD VERSION_LESS 20)
+  message(FATAL_ERROR "You are trying to build podio against a version of ROOT that has not been built with a sufficient c++ standard. podio requires c++20 or higher")
 endif()
 if(NOT ROOT_CXX_STANDARD VERSION_EQUAL CMAKE_CXX_STANDARD)
   message(WARNING "You are trying to build podio with a different c++ standard than ROOT. C++${CMAKE_CXX_STANDARD} was required but ROOT was built with C++${ROOT_CXX_STANDARD}")
 endif()
 
-# ROOT only sets usage requirements from 6.14, so for
-# earlier versions need to hack in INTERFACE_INCLUDE_DIRECTORIES
-if(ROOT_VERSION VERSION_LESS 6.14)
-  set_property(TARGET ROOT::Core APPEND PROPERTY INTERFACE_INCLUDE_DIRECTORIES "${ROOT_INCLUDE_DIRS}")
-endif()
 list(APPEND PODIO_IO_HANDLERS ROOT)
 
 # python setup (including python package discovery and install dir)

cmake/podioConfig.cmake.in

@@ -49,12 +49,6 @@ endif()
 if(NOT TARGET podio::podio)
   include("${CMAKE_CURRENT_LIST_DIR}/podioTargets.cmake")
   include("${CMAKE_CURRENT_LIST_DIR}/podioMacros.cmake")
-
-  # ROOT only sets usage requirements from 6.14, so for
-  # earlier versions need to hack in INTERFACE_INCLUDE_DIRECTORIES
-  if(ROOT_VERSION VERSION_LESS 6.14)
-    set_property(TARGET podio::podio APPEND PROPERTY INTERFACE_INCLUDE_DIRECTORIES "${ROOT_INCLUDE_DIRS}")
-  endif()
 endif()
 
 check_required_components(podio)

doc/links.md

@@ -194,18 +194,15 @@ default handle types. This is ensured through `static_assert`s in the
 `GetDefaultHandleType` helper templates are used to retrieve the correct type
 from any `FromT` regardless of whether it is a mutable or a default handle type
 With this in mind, effectively all mutating operations on `Link`s are
-defined using [*SFINAE*](https://en.cppreference.com/w/cpp/language/sfinae)
-using the following template structure (taking here `setFrom` as an example)
+defined using the following template structure (taking here `setFrom` as an example)
 
 ```cpp
-template <typename FromU,
-          typename = std::enable_if_t<Mutable &&
-                                      std::is_same_v<detail::GetDefaultHandleType<FromU>, FromT>>>
-void setFrom(FromU value);
+template <typename FromU>
+requires(Mutable&& std::is_same_v<detail::GetDefaultHandleType<FromU>, FromT>&&
+             detail::isDefaultHandleType<FromU>) void setFrom(FromU value);
 ```
 
-This is a SFINAE friendly way to ensure that this definition is only viable if
-the following conditions are met
+Compilation will fail unless the following conditions are met
 - The object this method is called on has to be `Mutable`. (first part inside the `std::enable_if`)
 - The passed in `value` is either a `Mutable` or default class of type `FromT`. (second part inside the `std::enable_if`)
 

include/podio/Frame.h

@@ -2,7 +2,6 @@
 #define PODIO_FRAME_H
 
 #include "podio/CollectionBase.h"
-#include "podio/CollectionBufferFactory.h"
 #include "podio/CollectionIDTable.h"
 #include "podio/FrameCategories.h" // mainly for convenience
 #include "podio/GenericParameters.h"
@@ -23,17 +22,13 @@
 
 namespace podio {
 
-/// Alias template for enabling overloads only for Collections
+/// Concept for enabling overloads only for Collection r-values
 template <typename T>
-using EnableIfCollection = typename std::enable_if_t<isCollection<T>>;
+concept CollectionRValueType = collectionType<T> && !std::is_lvalue_reference_v<T>;
 
-/// Alias template for enabling overloads only for Collection r-values
+/// Concept for enabling overloads for r-values
 template <typename T>
-using EnableIfCollectionRValue = typename std::enable_if_t<isCollection<T> && !std::is_lvalue_reference_v<T>>;
-
-/// Alias template for enabling overloads for r-values
-template <typename T>
-using EnableIfRValue = typename std::enable_if_t<!std ::is_lvalue_reference_v<T>>;
+concept RValueType = !std::is_lvalue_reference_v<T>;
 
 namespace detail {
   /// The minimal interface for raw data types
@@ -165,7 +160,7 @@ class Frame {
   /// @tparam FrameDataT Arbitrary data container that provides access to the
   ///                    collection buffers as well as the metadata, when
   ///                    requested by the Frame.
-  template <typename FrameDataT, typename = EnableIfRValue<FrameDataT>>
+  template <RValueType FrameDataT>
   Frame(FrameDataT&&);
 
   /// A Frame is move-only
@@ -193,7 +188,7 @@ class Frame {
   ///
   /// @returns      A const reference to the collection if it is available or to
   ///               an empty (static) collection
-  template <typename CollT, typename = EnableIfCollection<CollT>>
+  template <collectionType CollT>
   const CollT& get(const std::string& name) const;
 
   /// Get a collection pointer from the Frame by name.
@@ -218,7 +213,7 @@ class Frame {
   ///
   /// @returns      A const reference to the collection that has just been
   ///               inserted
-  template <typename CollT, typename = EnableIfCollectionRValue<CollT>>
+  template <CollectionRValueType CollT>
   const CollT& put(CollT&& coll, const std::string& name);
 
   /// (Destructively) move a collection into the Frame.
@@ -271,8 +266,9 @@ class Frame {
   ///              is supported by GenericParameters
   /// @param key    The name under which this parameter should be stored
   /// @param values The values of the parameter. A copy will be put into the Frame
-  template <typename T, typename = std::enable_if_t<detail::isInTuple<T, SupportedGenericDataTypes>>>
-  inline void putParameter(const std::string& key, std::initializer_list<T>&& values) {
+  template <typename T>
+  requires detail::isInTuple<T, SupportedGenericDataTypes> inline void putParameter(const std::string& key,
+                                                                                    std::initializer_list<T>&& values) {
     putParameter<std::vector<T>>(key, std::move(values));
   }
 
@@ -374,11 +370,11 @@ template <typename FrameDataT>
 Frame::Frame(std::unique_ptr<FrameDataT> data) : m_self(std::make_unique<FrameModel<FrameDataT>>(std::move(data))) {
 }
 
-template <typename FrameDataT, typename>
+template <RValueType FrameDataT>
 Frame::Frame(FrameDataT&& data) : Frame(std::make_unique<FrameDataT>(std::move(data))) {
 }
 
-template <typename CollT, typename>
+template <collectionType CollT>
 const CollT& Frame::get(const std::string& name) const {
   const auto* coll = dynamic_cast<const CollT*>(m_self->get(name));
   if (coll) {
@@ -400,7 +396,7 @@ inline void Frame::put(std::unique_ptr<podio::CollectionBase> coll, const std::s
   }
 }
 
-template <typename CollT, typename>
+template <CollectionRValueType CollT>
 const CollT& Frame::put(CollT&& coll, const std::string& name) {
   const auto* retColl = static_cast<const CollT*>(m_self->put(std::make_unique<CollT>(std::move(coll)), name));
   if (retColl) {

include/podio/UserDataCollection.h

@@ -9,11 +9,11 @@
 
 #define PODIO_ADD_USER_TYPE(type)                                                                                      \
   template <>                                                                                                          \
-  constexpr const char* userDataTypeName<type>() {                                                                     \
+  consteval const char* userDataTypeName<type>() {                                                                     \
     return #type;                                                                                                      \
   }                                                                                                                    \
   template <>                                                                                                          \
-  constexpr const char* userDataCollTypeName<type>() {                                                                 \
+  consteval const char* userDataCollTypeName<type>() {                                                                 \
     return "podio::UserDataCollection<" #type ">";                                                                     \
   }
 
@@ -31,12 +31,12 @@ using EnableIfSupportedUserType = std::enable_if_t<detail::isInTuple<T, Supporte
 /// helper template to provide readable type names for basic types with macro
 /// PODIO_ADD_USER_TYPE(type)
 template <typename BasicType, typename = EnableIfSupportedUserType<BasicType>>
-constexpr const char* userDataTypeName();
+consteval const char* userDataTypeName();
 
 /// Helper template to provide the fully qualified name of a UserDataCollection.
 /// Implementations are populated by the PODIO_ADD_USER_TYPE macro.
 template <typename BasicType, typename = EnableIfSupportedUserType<BasicType>>
-constexpr const char* userDataCollTypeName();
+consteval const char* userDataCollTypeName();
 
 PODIO_ADD_USER_TYPE(float)
 PODIO_ADD_USER_TYPE(double)