At least one other compiler does in fact require the bare definition to link properly, and doesn't generate it automatically as an enhancement. So I need to make these definitions conditional based on the platform (and perhaps the exact compiler version? That's why I like to use the existing config knowledge base!)
I see that Boost has BOOST_STATIC_CONSTANT but that is for compilers that don't have the in-class initialization at all.
So if Boost is using such constructs, how does it deal with the linker idiosyncrasy?
You could always not initialize inline and therefore always supply a separate definition.
Which would prevent them being used as constant-expressions? In fact even when initialized inline, an out of line definition should always be provided as different compilers have different ideas about what constitutes "use" of the variable (rather than just the value). MSVC pretty much never requires an out-of-line definition for example, where as GCC will often generate linker errors if you don't provide it. HTH, John.