C++: Header-only project, static const non-integral

Question

I have a header-only project. Inside it I have a class. Inside it (or anywhere else actually) I would like to have constant data (enum values to string and

Answer 1

The simpler is

static T& global_t()
{ static T z = initializer; return z; }

global_t() can be used whereve a T value is required.

NOTE: In answer to rioki comment, we must also specify the function as inline if it is at global or namespace level (to avoid the "multiple instances" problem towards the linker).

The inline keyword is not necessary if the function is a template or is a class member-function (for which the inline definition is by default)

If the static T instantiation must be shared among different OS modules (read: DLLs) rioki is perfectly right, but -at that point- a header-only library makes no more sense.

---

Starting from C++17, the inline specifier can also be used on variables.

So, from C++17 onward, you can just write

inline T global_object = initializer;

You can also use inline for static members of function, to provide inline initialization, like

class Class
{
    static inline Type static_object_name = initializer;
};