| name | google-cpp-style |
| description | Enforce the Google C++ Style Guide as adopted by Cytnx when writing, reviewing, or refactoring C++ or CUDA (.cpp/.hpp/.cu/.cuh) code. Use when creating new C++/CUDA files or symbols, naming types/functions/variables, choosing parameter-passing conventions, or reviewing a C++ diff for style. Covers Cytnx's naming rules (snake_case for new code, no leading underscore, trailing-underscore in-place mutators), pass-scalars-by-value, includes, error handling, and the clang-format v14 boundary. |
Google C++ style (as adopted by Cytnx)
Cytnx uses the Google C++ Style Guide as its baseline — .clang-format is
BasedOnStyle: Google and the maintainers deliberately picked Google style for
the project. The full guide is at
https://google.github.io/styleguide/cppguide.html. This skill distills the
rules that matter for review plus the Cytnx-specific overrides that win where
they diverge from stock Google style.
Order of precedence
- The file you are editing. If a file already uses a consistent local
convention, match it — never mix two styles inside one file.
- Cytnx overrides (below) — for new files, and for already-inconsistent
("messy") files, where these beat both the file and stock Google.
- Google C++ Style Guide for everything the above do not cover.
Do not rewrite an existing file to "fix" its style as a side effect of an
unrelated change — that is churn. Apply these rules to new code; much of the
existing tree predates the convention.
Cytnx overrides (take precedence over stock Google)
- No leading underscore in new code — strict.
_foo, _impl, _Load are
the old private-member / internal convention and are being retired (#836).
New members, helpers, and locals must not start with _.
- A trailing underscore marks an in-place mutator that returns
*this —
Add_, contiguous_, Inv_, Exp_. This is Cytnx's meaning and differs
from Google, where a trailing underscore denotes a data member. Do not give
member variables a trailing underscore, and do not "correct" the existing
mutators.
- snake_case for new identifiers. Functions, variables, and members in new
code are
lower_snake_case (#836). Type names stay PascalCase (UniTensor,
Storage). Much existing code is CamelCase/mixed — match the file when
editing it, use snake_case when adding new files.
- Pass small/scalar types by value, not
const&. Built-ins, enums,
cytnx_uint64, cytnx_int64, Scalar, and complex scalars (complex<double>
/ cytnx_complex128) go by value. For a Cytnx scalar a reference is never
faster: const& forces a stack spill plus pointer indirection, whereas a value
can ride in registers. Reserve const& for genuinely large objects — Tensor,
Storage, UniTensor, std::vector, std::string, containers.
- C++20 / CUDA 20 are available and expected (
CMAKE_CXX_STANDARD 20,
CMAKE_CUDA_STANDARD 20). Use them; never add C++17 back-compat guards or
workarounds (see GEMINI.md).
Google naming reference (baseline)
- Types (class/struct/enum/alias/type template param):
PascalCase, no
underscores — UniTensor, BlockStore.
- Constants (
constexpr/const, static storage): kCamelCase —
kDefaultBondDim.
- Macros:
ALL_CAPS_WITH_UNDERSCORES — but avoid macros; prefer constexpr.
- Namespaces: short,
lower_case — cytnx, cytnx::linalg.
- Files:
lower_case (underscores allowed); headers .hpp, sources .cpp,
CUDA .cu/.cuh.
- Variables/functions: stock Google uses
CamelCase functions and snake_case
variables — Cytnx overrides functions to snake_case for new code (above).
Design & correctness rules worth enforcing
- Includes: include what you use; forward-declare in headers instead of
pulling heavy includes.
.clang-format has SortIncludes: false, so do not
reorder existing include blocks — only place new includes sensibly.
- Const-correctness: mark methods
const when they do not mutate; mark
single-argument constructors explicit.
- Ownership: prefer values and RAII; owning heap resources use smart
pointers; a raw pointer/reference is non-owning.
- Use
nullptr (not NULL/0); override/final on virtual overrides;
enum class over unscoped enums for new code.
- No
using namespace in headers — keep public headers self-contained.
- Errors: raise Cytnx errors with
cytnx_error_msg(cond, "fmt", …) (throws
cytnx::error, surfaced in Python as cytnx.CytnxError; the function name
comes from CYTNX_FUNC_NAME) rather than a bare throw or assert — this is
the project idiom.
Formatting is not your job
.clang-format (pinned to v14, BasedOnStyle: Google, column 100,
IndentWidth: 2) owns every whitespace, brace, and wrapping decision. Never
hand-format and never comment on layout — run pre-commit run --files <changed>
and let the hook settle it (CI's clang-format-check uses v14; a different
version reflows and fails CI). Review naming, design, and correctness — the
things a formatter cannot check.
Review checklist
