[Boris]
| I think the bulk of the unnecessary recompilations will come from
| modifying implementation details (e.g., non-inline function bodies).
| And that hash idea would have worked except for the pesky line/column
| numbers. So it seems like the best solution is to keep one's
| implementation details in module implementation units.

I suspect this might make a key differentiator from the C# experience: C++ provides means to separate interface from implementation details if one choses to.

-- Gaby