cpp-coding

# C++ Coding ## Language C++20. Prefer standard library over custom implementations when appropriate. ## Naming conventions | Element | Style | Example | |---------|-------|---------| | Functions | `lowerCamelCase` | `processStreamData()`, `handleWindowClose()` | | Variables | `lowercase_with_underscores` | `event_count`, `window_start` | | Classes | `PascalCase` | `StorageStream`, `AggregatedDataVariants` | | Constants | `PascalCase` or `UPPER_CASE` | Per existing codebase convention | | Namespaces | `PascalCase` | `DB::Streaming` | ## Proton fences ```cpp /// proton: starts if (isStreamingQuery()) { handleStreamingPath(); } /// proton: ends ``` - [ ] Use ONLY in ClickHouse-inherited code (upstream-synced files) - [ ] NEVER fence in `src/Storages/Stream/` or `namespace DB::Streaming` - [ ] NEVER nest fences ## IProcessor pattern (streaming transforms) All streaming transforms in `src/Processors/Transforms/Streaming/` follow: ```cpp class MyTransform : public IProcessor { Status prepare() override; // O(1), non-blocking, check readiness void work() override; // Do actual processing }; ``` Stateful processors MUST also implement: - [ ] `hasState()` → return true - [ ] `checkpoint(CheckpointContextPtr)` → serialize state - [ ] `recover(CheckpointContextPtr)` → restore from checkpoint ## Formatting Only formats changed code blocks (not entire files). Uses `.clang-format` config at repo root. The configured brace style is Allman-like: opening braces normally go on a new line. ```bash git clang-format # format unstaged changes in-place git clang-format --staged # format staged changes in-place git clang-format --diff # dry-run: show what would change git clang-format <commit> # format changes since <commit> ``` ## Comments Use `///`. Explain **why**, not what: ```cpp /// Use 10 seconds to allow late events watermark_delay = 10; ```