Quick Q: Undefined reference to static constexpr char[]
Quick A: this is no longer an issue with C++17.
Recently on SO:
Undefined reference to static constexpr char[]
Add to your cpp file:
constexpr char foo::baz[];Reason: You have to provide the definition of the static member as well as the declaration. The declaration and the initializer go inside the class definition, but the member definition has to be separate.

 We’re in the final countdown to this year’s CppCon, which starts on September 16. To whet your appetite for this year’s conference, here’s another of the top-rated talks from last year. Enjoy – and
We’re in the final countdown to this year’s CppCon, which starts on September 16. To whet your appetite for this year’s conference, here’s another of the top-rated talks from last year. Enjoy – and  We’re in the final countdown to this year’s CppCon, which starts on September 16. To whet your appetite for this year’s conference, here’s another of the top-rated talks from last year. Enjoy – and
We’re in the final countdown to this year’s CppCon, which starts on September 16. To whet your appetite for this year’s conference, here’s another of the top-rated talks from last year. Enjoy – and