Notes

A promise: “this function will never throw an exception.”

void resetCounter() noexcept { count = 0; }

Why containers care

Node(Node&& other) noexcept { ... }   // move constructor

std::vector needs to move its elements when it grows. If the move constructor might throw partway through, a failed move could leave the vector in a corrupted, half-moved state — so vector plays it safe and copies instead. Mark the move constructor noexcept and vector actually uses it, getting the performance it was written for in the first place.

Break the promise, and the program terminates

If a noexcept function throws anyway, std::terminate() is called immediately — no stack unwinding, no catch block gets a chance. Only mark something noexcept if certain.

Related

Rule of Five and deep copy