Cpp Patterns

C++ Patterns

Use this skill for day-to-day modern C++ (C++20+) with a bias for safety, clarity, and maintainable APIs.

If your primary task is test architecture/debugging, activate cpp-testing alongside this skill.

When to activate

• Writing new C++ modules/libraries/services
• Reviewing PRs for ownership, lifetime, and exception safety
• Refactoring for cleaner interfaces and fewer footguns
• Introducing RAII, smart pointers, and standard library algorithms

Outcome expectations

• APIs encode ownership and lifetime intent directly in types.
• Resource cleanup is deterministic (RAII) and exception-safe.
• Error behavior is consistent per layer (no mixed ad-hoc strategy).
• Concurrency code has explicit stop/cancellation and race-checking plan.

Core rules (high signal)

• Prefer RAII for resource ownership; avoid raw new/delete.
• Use value types by default; use references/pointers to express optionality and non-ownership.
• Use std::unique_ptr for exclusive ownership; std::shared_ptr only when shared ownership is required.
• Prefer standard algorithms over hand-written loops when it improves clarity.
• Keep APIs small; make invalid states unrepresentable where feasible.
• Define clear error strategy: exceptions vs std::expected-style returns vs status codes.

Recommended workflow

1. Clarify ownership and lifetime boundaries first (handles, buffers, views, async captures).
2. Design the public API around value semantics and explicit contracts.
3. Implement with RAII wrappers and Rule-of-Zero defaults.
4. Add warnings/sanitizers/static analysis early in the build.
5. Review for footguns (dangling views, iterator invalidation, detached threads).

Quick review checklist

• Ownership is explicit (who allocates, who frees)
• No leaks or dangling refs (temporaries, string_view, iterator invalidation)
• Rule of Zero is used; special members defined only when needed
• const correctness is consistent
• No surprising implicit conversions; use explicit
• Concurrency code has a cancellation/stop strategy
• Error semantics and exception guarantees are documented

Common anti-patterns to reject

• Owning raw pointers in public APIs
• Returning/storing std::string_view tied to temporary storage
• Detached threads that capture this without a lifetime model
• Broad catch (...) blocks that hide failure context
• Exposing mutable shared state without synchronization policy

Resources

Load on demand:

• references/ownership-raii.md — ownership rules, RAII patterns, smart pointers, lifetime
• references/core-guidelines.md — distilled C++ Core Guidelines pointers
• references/api-design.md — interface design, value semantics, error strategy
• references/concurrency.md — jthread, mutex, atomic, condition_variable, stop_token, race detection
• references/tooling-build.md — compiler warnings, sanitizers, static analysis, binary inspection (MinGW/objdump, MSVC/dumpbin, Linux tools), CMake hygiene