I got the basic structure down pretty fast but fumbled on the sequencing inside move assignment.
Start by clarifying the requirements and constraints (e.g., C++ version, exception safety). Then outline the class design, emphasizing move semantics and self-move-assignment handling. Finally, discuss implementation details, including the rule of five and potential pitfalls.
Pro tip: Mention that self-move-assignment can be handled by checking for self-assignment or by using the copy-and-swap idiom, but note that the latter requires a swap function. Also, consider using std::exchange for concise move operations.
Ask about the expected C++ standard, exception safety guarantees, and whether the pointer should support custom deleters or arrays.
Define the class template with a raw pointer member. Declare constructors, destructor, move constructor, move assignment, and deleted copy operations. Include get, release, reset, operator*, and operator->.
Implement move constructor and move assignment to transfer ownership. For move assignment, handle self-assignment by checking if this != &other, or use a swap-based approach. Ensure the old resource is released.
Implement destructor to delete the pointer. Implement get, release, reset, and dereference operators. Ensure reset deletes the current pointer and takes ownership of the new one.
Mention testing scenarios: self-move-assignment, move from, reset, release, and exception safety. Consider using static_assert to enforce move-only semantics.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.
Start by clarifying requirements and constraints, then outline the design using raw storage and placement new. Walk through each operation, emphasizing exception safety, move semantics, and the separation of size and capacity. Conclude with trade-offs and potential optimizations.
Pro tip: Mention that you would use std::aligned_storage or a char buffer with proper alignment, and that you'd implement strong exception guarantees for push_back and reserve. This shows you understand low-level memory management and production-quality code.
Ask about alignment requirements, exception safety guarantees, and whether the container should support non-default-constructible types. Confirm that raw storage means no default construction of unused slots.
Define member variables: pointer to raw storage, size, capacity. Explain how to allocate aligned memory (e.g., using operator new or std::aligned_alloc) and deallocate it.
Describe push_back using placement new and handling reallocation; pop_back calling destructor; reserve allocating new storage and moving elements; clear destroying elements and setting size to 0.
For copy constructor/assignment, allocate new storage and copy-construct elements. For move, steal the pointer and reset source. Discuss noexcept and self-assignment.
Explain how to provide strong exception guarantee for push_back (e.g., copy-and-swap) and basic guarantee for others. Mention performance considerations and alternatives like std::vector.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.
Start by defining copy and move semantics in terms of resource ownership and performance, then walk through your two implementations to pinpoint where each applies. Explain the smart pointer's move-only design by contrasting exclusive ownership with the vector's need for both copy and move to support flexible usage.
Pro tip: Emphasize that move semantics are an optimization, not a replacement for copy semantics—this shows you understand when each is appropriate and avoids overusing moves. Also, mention that move-only types like smart pointers enforce correctness by preventing accidental copies of unique resources.
Explain that copy semantics duplicate an object's resources, while move semantics transfer ownership, leaving the source in a valid but unspecified state. Highlight the performance and ownership implications.
Identify specific classes/functions in your two implementations where copy and move occur. For example, in a vector-like class, copy happens in the copy constructor and move in the move constructor; in a smart pointer, move occurs in the move constructor and move assignment.
Discuss that a smart pointer typically models exclusive ownership (like unique_ptr), so copying would lead to double deletion or ambiguity. Moving transfers ownership safely.
Describe that a vector manages a dynamic array and may need to copy elements for operations like copying the vector itself, but also benefits from moving elements during reallocation or when the vector is moved. This flexibility supports both value semantics and efficient resource transfer.
Summarize that move-only types enforce unique ownership and prevent costly or incorrect copies, while types supporting both offer versatility at the cost of potential accidental copies. Relate this to design decisions in your implementations.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.
Explain that std::vector must provide the strong exception guarantee during reallocation, so it can only move elements if the move constructor is noexcept; otherwise, it copies to allow rollback. Then describe the specific failure scenario if moves could throw.
Pro tip: Mention that this is why it's crucial to mark move constructors noexcept when possible, and that types with throwing moves can silently degrade performance in vectors.
Clarify that std::vector reallocation must offer the strong exception guarantee: if an exception is thrown, the vector remains unchanged.
Describe how vector allocates new storage, then transfers elements from old to new storage, and finally deallocates old storage.
Explain that moving modifies the source, so if a move throws mid-transfer, the original elements may be left in a valid but unspecified state, making rollback impossible.
Explain that if the move constructor is not noexcept, vector uses copy construction instead, because copies leave the source intact, allowing rollback.
Summarize that this design ensures exception safety at the cost of performance, and encourage marking move constructors noexcept when safe.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.
Start by clarifying the requirements: custom deleter support with zero overhead for the default case. Then propose a design using a type-erased deleter stored only when needed, such as a union or a template specialization that avoids storing a deleter for the default case. Explain how this achieves zero overhead by not increasing the size of the smart pointer and not adding runtime branches for the common case.
Pro tip: Mention that this is exactly how std::unique_ptr is implemented in major standard libraries: it uses the empty base optimization (EBO) or a compressed pair to store the deleter only when it's not empty, and for the default deleter (std::default_delete), it's an empty class, so no extra space is used. This shows you understand real-world implementations.
Confirm that 'no runtime overhead' means no extra memory footprint and no extra branches for the default case. Also confirm that custom deleters should be supported without affecting the default case's performance.
Discuss possible approaches: template parameter for deleter (like unique_ptr), type erasure (like shared_ptr), or a hybrid. Explain trade-offs: templates give zero overhead but increase code size; type erasure adds overhead but allows runtime flexibility.
Suggest using a template parameter for the deleter, defaulting to a stateless deleter. Use empty base optimization or compressed pair to avoid storing the deleter when it's empty. For stateful deleters, store them as members, but only when needed.
Detail that the default deleter is an empty class, so with EBO, the smart pointer's size is just the pointer. Also, the delete call is statically dispatched, so no virtual function or branch is needed.
Mention that this design requires the deleter type to be part of the smart pointer's type, which may not be suitable for all use cases. If runtime polymorphism is needed, consider a type-erased wrapper but acknowledge the overhead.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.
Pretty quick answer: any reallocation invalidates everything, so push_back when size equals capacity is the main culprit.
Start by clearly stating the iterator/reference invalidation rules for your vector implementation, then systematically compare them to std::vector's rules. Highlight any deliberate design choices and trade-offs, and conclude with the practical implications for users.
Pro tip: Emphasize that iterator invalidation is a critical API contract; documenting and testing it thoroughly shows you understand the importance of predictable behavior in container design.
List the operations that invalidate iterators and references in your implementation, such as reallocation on push_back, insert, erase, reserve, resize, and shrink_to_fit.
Explain how std::vector handles the same operations, noting similarities and differences, especially regarding reallocation and element shifting.
Discuss why your implementation may differ, such as different growth strategies, memory management, or API guarantees, and the trade-offs involved.
Describe how these invalidation rules affect usage, such as the need to refresh iterators after modifications, and any safety mechanisms you provide.
Mention how you ensure correctness through tests and documentation, and invite further questions about specific scenarios.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.