constexpr static data member giving undefined reference error

Question

I\'m working on a kernel and I want to make my static data member constexpr so I can have its values in an enum class. However, if I do so I get an

Answer 1

A static data member shall be defined outside the class if it is odr-used---period. There are no exceptions to this rule.

In the case that the data member is constexpr, it must also be initialized inside the class definition. However this does not abrogate the requirement to define it outside the class.

Correct code:

class Terminal
{
    constexpr static uint32_t col_map[16] = { /* ... */ };
    // ...
};
constexpr uint32_t Terminal::col_map[16]; // definition

It's counterintuitive, but that's just the way it is.