source is C++11; benchmark is C++17

[egberts]

The source code compiles fine under C++ 2011,
But the benchmark can only use C++ 2017.

For someone who only has C++ 2011, this cmake fails overall due to this inability compile benchmark.

[cjgdev]

I was not (knowingly) using any features of C++17 (which at the time of writing, was not yet standardised). Can you please share details of platform, cmake version, and compiler, and I'll do my best to resolve for you.