Draft: adding cpp version of codes

What is the new feature

Creating the C++ version of existing code

The people involved in porting the existing codes to C++ are @b382190, @b382899, @m301159, @k202204, @k202194, @k202174 and @k202170

Mandatory steps before review

• Gitlab CI passes (Hint: use make format for linting)
• New feature is covered by additional unit tests
• Mark the merge request as ready by removing Draft:

Mandatory steps before merge

• Reviewed by a maintainer
• Incorporate review suggestions
• Remember to edit the commit message and select the proper changelog category (feature/bugfix/other)
• Prior to merging, please remove any boilerplate from the MR description, retaining only the Please describe your feature in a couple of words and describe important implementation details of the feature section to maintain

You are not supposed to merge this request by yourself, the maintainers of libiconmath take care of this action!

src/interpolation/CMakeLists.txt

@@ -13,6 +13,7 @@ add_library(
   iconmath-interpolation
   mo_lib_interpolation_scalar.F90
   mo_lib_interpolation_vector.F90
+  mo_lib_interpolation_vector.cpp
   mo_lib_intp_rbf.F90)
 
 add_library(${PROJECT_NAME}::interpolation ALIAS iconmath-interpolation)
@@ -55,10 +56,20 @@ target_include_directories(
     $<INSTALL_INTERFACE:$<$<COMPILE_LANGUAGE:Fortran>:$<INSTALL_PREFIX>/${CMAKE_INSTALL_INCLUDEDIR}>>
     # Path to internal include directory
     $<BUILD_INTERFACE:$<$<COMPILE_LANGUAGE:Fortran>:${PROJECT_SOURCE_DIR}/include>>
+    # Path to the internal C/C++ headers (for testing): Requires CMake 3.15+ for
+    # multiple compile languages
+    # https://cmake.org/cmake/help/latest/manual/cmake-generator-expressions.7.html
+    $<BUILD_INTERFACE:$<$<COMPILE_LANGUAGE:C,CXX>:${CMAKE_CURRENT_SOURCE_DIR}>>
+  PRIVATE
+    # Path to config.h (for C and C++ only): Requires CMake 3.15+ for multiple
+    # compile languages
+    # https://cmake.org/cmake/help/latest/manual/cmake-generator-expressions.7.html
+    $<BUILD_INTERFACE:$<$<COMPILE_LANGUAGE:C,CXX>:${CMAKE_CURRENT_BINARY_DIR}>>
 )
 
 target_link_libraries(iconmath-interpolation PUBLIC fortran-support::fortran-support)
 target_link_libraries(iconmath-interpolation PUBLIC iconmath-support)
+target_link_libraries(iconmath-interpolation PRIVATE Kokkos::kokkos)
 
 install(TARGETS iconmath-interpolation EXPORT "${PROJECT_NAME}-targets")