error: type/value mismatch at argument 1 in template parameter list for ‘template<class _Tp> struct std::remove_const’

[brighton36]

It seems that I'm getting the following errors when trying to compile this library:

cderose@cderose-EP45-UD3P ~/D/w/cpp-slim> make
g++ -Wall -Wconversion -std=c++14 -g --coverage -Iinclude/slim -Isource -c  -MMD -MP source/Template.cpp -o obj/lib/source/Template.cpp.o
In file included from include/slim/expression/../types/Enumerable.hpp:3,
                 from include/slim/expression/../types/Hash.hpp:3,
                 from include/slim/expression/Scope.hpp:4,
                 from include/slim/Template.hpp:3,
                 from source/Template.cpp:1:
include/slim/Function.hpp: In function ‘slim::ObjectPtr slim::detail::call_unpacked(slim::Object*, RetType (SelfType::*)(Args ...), const FunctionArgs&, slim::detail::Indices<indices ...>)’:
include/slim/Function.hpp:66:86: error: type/value mismatch at argument 1 in template parameter list for ‘template<class _Tp> struct std::remove_const’
   66 |                 (slim::unpack_arg<std::remove_const<std::remove_reference<Args>::type>::type>(args[indices])...));
      |                                                                                      ^
include/slim/Function.hpp:66:86: note:   expected a type, got ‘std::remove_reference<Args>::type’
include/slim/Function.hpp: In function ‘slim::ObjectPtr slim::detail::free_call_unpacked(slim::Object*, RetType (*)(SelfType*, Args ...), const FunctionArgs&, slim::detail::Indices<indices ...>)’:
include/slim/Function.hpp:101:89: error: type/value mismatch at argument 1 in template parameter list for ‘template<class _Tp> struct std::remove_const’
  101 |                     slim::unpack_arg<std::remove_const<std::remove_reference<Args>::type>::type>(args[indices])...));
      |                                                                                         ^
include/slim/Function.hpp:101:89: note:   expected a type, got ‘std::remove_reference<Args>::type’
make: *** [makefile:34: obj/lib/source/Template.cpp.o] Error 1

Note that I had to change the Makefile's CFLAGS to compile for C++14, to get this far: "-std=c++14"

Here's the version of g++ that I'm using:

cderose@cderose-EP45-UD3P ~/D/w/cpp-slim> g++ -v
Using built-in specs.
COLLECT_GCC=g++
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/9/lto-wrapper
OFFLOAD_TARGET_NAMES=nvptx-none:hsa
OFFLOAD_TARGET_DEFAULT=1
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu 9.2.1-9ubuntu2' --with-bugurl=file:///usr/share/doc/gcc-9/README.Bugs --enable-languages=c,ada,c++,go,brig,d,fortran,objc,obj-c++,gm2 --prefix=/usr --with-gcc-major-version-only --program-suffix=-9 --program-prefix=x86_64-linux-gnu- --enable-shared --enable-linker-build-id --libexecdir=/usr/lib --without-included-gettext --enable-threads=posix --libdir=/usr/lib --enable-nls --enable-bootstrap --enable-clocale=gnu --enable-libstdcxx-debug --enable-libstdcxx-time=yes --with-default-libstdcxx-abi=new --enable-gnu-unique-object --disable-vtable-verify --enable-plugin --enable-default-pie --with-system-zlib --with-target-system-zlib=auto --enable-multiarch --disable-werror --with-arch-32=i686 --with-abi=m64 --with-multilib-list=m32,m64,mx32 --enable-multilib --with-tune=generic --enable-offload-targets=nvptx-none,hsa --without-cuda-driver --enable-checking=release --build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=x86_64-linux-gnu
Thread model: posix
gcc version 9.2.1 20191008 (Ubuntu 9.2.1-9ubuntu2)