[account42]

Yes, smart pointers don't mean you can entirely stop thinking about ownership and lifetimes but they let you express that ownership in an explicit way with some compiler-enforced protections against mistakes.

> I have never seen a complex data structure where unique_ptr is really used.

What's a "complex" data structure? Anyway, I'd expect to see unique_ptr more in user code rather than in library implementations of data structures where where relatively minor concerns might warrant an ad-hoc implementation even if you could use unique_ptr. In many cases it's probably just that the implementations precede the standardized smart pointers.