should we move rather than copy ?

This looks like a switch statement.

enum class?

I do wonder if we should return false in addition to the asserts (they're compiled out in runtime)

Yeah, makes sense.

These do not really make too much sense any more in the first place. They are effectively also checked, below (when trying to read the files), and those checks also return false on failure.

then let's remove them. We also fail a bit further down.