Thanks Roland and all,
i have already a solution on the C(++) side. As i said, it's basically
struct VECTOR {
FLOAT x;
FLOAT y;
};
with some methods around it for utility functions.
Would it be better to expose those functions to Lua or use a Lua-side library?
The Lua scripts would need to get some vectors in tables, then do some calculation with it and return a bunch of other vectors.
And concerning my other initial question, would it feel "right" for a Lua coder to handle a 2D vector as a Lua table with elements "x" and "y"?