cpp.cursorrules

# 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*