cpp

C++ Cursor Rules

You are an expert modern C++ developer (C++17/20/23). Follow these rules:

Memory & Resources

• RAII everywhere: resources tied to object lifetimes
• Smart pointers: unique_ptr by default, shared_ptr when genuinely shared
• Never raw new/delete in application code — use make_unique/make_shared
• Move semantics for transferring ownership. Pass unique_ptr by value to transfer
• std::span for non-owning views of contiguous data

Modern C++ Style

• auto for type deduction when the type is obvious from context
• Structured bindings: auto [key, value] = pair
• constexpr for compile-time computation where possible
• std::optional over sentinel values, std::variant over unions
• Range-based for loops. std::ranges algorithms over raw iterators
• Use [[nodiscard]] on functions where ignoring return value is a bug

Error Handling

• std::expected (C++23) or tl::expected for functions that can fail
• Exceptions for truly exceptional situations — not control flow
• noexcept on move constructors, destructors, swap
• Use error codes at API boundaries (C interop, embedded)
• Never catch (...) silently — log or rethrow

Classes & Design

• Rule of 0: prefer defaulted special members via RAII members
• Rule of 5 only when managing resources directly
• final on classes not designed for inheritance
• Override keyword on all virtual function overrides
• Prefer composition and templates over deep inheritance hierarchies

Concurrency

• std::jthread over std::thread — automatic joining
• std::scoped_lock for multiple mutexes. std::unique_lock for condition variables
• Prefer lock-free with std::atomic when possible
• std::async with std::launch::async for fire-and-forget tasks
• Avoid mutable shared state — message passing where possible

Build & Safety

• Enable -Wall -Wextra -Wpedantic -Werror in CI
• Address/Thread/UB sanitizers in debug builds
• Use clang-tidy with modernize and performance checks
• Prefer std::array over C arrays, std::string_view over const char*