How do move semantics and rvalue references improve performance?
Assesses fundamental understanding of C++ conventions, runtime behavior, and memory/performance considerations.
Hiring managers look for precision, avoidance of ambiguous jargon, and ability to explain trade-offs under real production conditions.
Copying large objects is expensive. Move semantics transfer ownership of a resource from a temporary (an rvalue) instead of copying, leaving the source in a valid but unspecified state. It relies on rvalue references (T&&) plus a move constructor and move assignment operator.
std::vector<std::string> make();
std::vector<std::string> v = make(); // move, not copy
std::string s = "long text";
std::vector<std::string> w;
w.push_back(std::move(s)); // s is left empty-ish
std::move is just a cast to an rvalue reference; it does not move anything by itself. Moves of standard containers are O(1) pointer swaps, not element-by-element copies.
The "rule of five" says that if you define a destructor, copy or move operation, define or delete all of them. Mark move operations noexcept so containers such as vector prefer them during reallocation. Never use a moved-from object except to assign or destroy it.
Candidate Response Strategy & Interview Tips
- Start with a concise one-sentence summary: Deliver a direct, confident answer first before expanding into nuances.
- Demonstrate real-world trade-offs: Discuss where this approach excels and when you would avoid it in production systems.
- Discuss complexity & edge cases: Proactively explain time/space complexity or boundary conditions (null values, scale limits).
- Prepare for interviewer follow-ups: Technical hiring panels frequently probe deeper into concurrency, backward compatibility, or alternative libraries.