EigenSerialize

Test repo for Eigen matrix serialization with boost

See SO for discussion and solution: https://stackoverflow.com/questions/54534047/eigen-matrix-boostserialization-c17

Somewhere in the code an Eigen type-trait gets instantiated which tries to access an incomplete type of boost::serialization. Totally strang. Works with C++11/14...??!

usr/local/include/Eigen/src/Core/util/ForwardDeclarations.h:32:
error: incomplete type ‘Eigen::internal::traits<boost::serialization::U>’ used in nested name specifier
enum { has_direct_access = (traits<Derived>::Flags & DirectAccessBit) ? 1 : 0,

The error occures whenever boost/serialization/shared_ptr.hpp is included - regardless if a shared_ptr is serialized or not. See line 15 in the main.cpp:

#include <boost/serialization/shared_ptr.hpp>

To compile use:

• G++: g++-7 -std=c++17 -o main.o main.cpp -lboost_serialization
• Clang: clang -std=c++17 -o main.o main.cpp -lboost_serialization -lstdc++

Seems to be compiler-related:

• GCC7/8 failes with the mesage above (regardless if --std=c++17 or --std=c++20)
• GCC6 works with --std=c++17
• Clang6 works with --std=c++17