Turn your LLM coding assistant into a C++26 specialist.
A Claude Code plugin (and standalone MCP server) that biases generation toward ISO/IEC 14882:2026 final-form idioms — reflection, contracts, senders, inplace_vector, #embed — even when your local clang hasn't caught up.
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Full plugin (Claude Code — skill + MCP + reviewer + hooks + slash command):
/plugin marketplace add parasxos/claude-plugins
/plugin install cpp26-adapter@parasxos/claude-plugins
MCP server only (any MCP-compatible client):
pip install cpp26-refSix concrete idiom shifts on the same prompts a vanilla LLM would answer with pre-C++26 patterns:
| You ask for… | Vanilla LLM emits | cpp26-adapter emits |
|---|---|---|
| enum → string | X-macros / magic_enum |
std::meta::enumerators_of(^^E) + template for |
| precondition | assert(x > 0) |
pre(x > 0) / contract_assert(...) |
| async pipeline | std::async(...) |
ex::just | ex::then | ex::sync_wait |
| fixed-capacity vector | boost::static_vector |
std::inplace_vector<T, N> |
| embed binary asset | objcopy / xxd / incbin |
#embed "asset.bin" |
| Nth pack element | std::get<N>(std::forward_as_tuple(args...)) |
args...[N] |
Vanilla falls back to X-macros. With cpp26-adapter — straight from P2996 reflection + P1306 expansion statements:
template <typename E> requires std::is_enum_v<E>
constexpr std::string_view enum_name(E v) {
template for (constexpr auto e :
std::define_static_array(std::meta::enumerators_of(^^E))) {
if (v == [: e :]) return std::meta::identifier_of(e);
}
return "<unknown>";
}No macros. No third-party dep. No codegen. More side-by-side examples (contracts, senders, #embed): docs/examples.md.
| Client | Recommended path |
|---|---|
| Claude Code | /plugin install (full plugin: skill + MCP + reviewer + hooks) |
| Claude Desktop | cpp26-ref MCP server via stdio (config below) |
| Cursor | cpp26-ref MCP server via stdio |
| VS Code (Cline / Continue) | cpp26-ref MCP server via stdio |
| Any other MCP client | cpp26-ref MCP server via stdio |
After /plugin install cpp26-adapter@parasxos/claude-plugins, everything wires itself up: the skill loads into context, the MCP starts on demand, the reviewer subagent is callable as @cpp26-reviewer, the hook lints on every C++ edit, and /cpp26-init is available.
Add to ~/Library/Application Support/Claude/claude_desktop_config.json (macOS) or %APPDATA%\Claude\claude_desktop_config.json (Windows):
{
"mcpServers": {
"cpp26-ref": {
"command": "cpp26-ref"
}
}
}Requires pip install cpp26-ref on a Python (≥3.11) reachable from the Claude Desktop process.
{
"mcpServers": {
"cpp26-ref": { "command": "cpp26-ref" }
}
}After install + restart, three sanity checks:
- Ask the assistant "write enum-to-string for
enum class E { A, B }" — the response should usestd::metareflection, not X-macros ormagic_enum. - (Full plugin only) Run
@cpp26-reviewer src/foo.cpp— should return a YAML report withstatus: pass | needs-changes | compiler-lag-only. - (Full plugin only) Run
/cpp26-initin an empty directory — the scaffoldedCMakeLists.txtshould build a#include <print>+std::print("hi\n")hello-world.
The cpp26-ref server exposes three stdio tools over MCP, in-memory over 216 indexed C++26 papers (no SQLite, no embeddings, no build step):
| Tool | Signature | Returns |
|---|---|---|
lookup_paper |
(paper_id: str) — e.g. "P2996" |
Full reference: title, problem statement, key syntax, canonical example, pre-C++26 equivalent, gotchas, related papers |
search |
(query: str, limit: int = 5) |
Top-N papers ranked by rapidfuzz partial-ratio against title + frontmatter |
compiler_status |
(paper_id: str) |
Per-compiler implementation status: none/partial/shipped × clang / gcc / msvc / clang-p2996 with version cutoffs |
Cold start ~352 ms. 17 tests pass under pytest mcp-server/tests.
Generate idiomatic C++26 code. Ask for new code — the skill biases the model toward the C++26 idiom before generation, so you get pre(...) instead of assert(...), std::execution instead of std::async, reflection instead of X-macros, without re-prompting.
Review existing code for C++26 modernization. Run @cpp26-reviewer src/foo.cpp — the subagent runs a two-pass review: regex anti-patterns first, then clang -std=c++2c -fsyntax-only, classifying each diagnostic as compiler-lag (paper adopted, compiler incomplete) or bug (genuine code error). You see both axes side by side.
Initialize a new C++26 project. Run /cpp26-init — scaffolds CMakeLists.txt (CXX_STANDARD 26, -std=c++2c, CMAKE_EXPORT_COMPILE_COMMANDS ON), .clangd, and .cpp26-adapter.yaml.
Get authoritative paper references. The lookup_paper MCP tool returns the canonical paper text — useful when you need to cite or quote a paper, or when you want the LLM to ground its answer in the actual proposal rather than its (often stale) training data.
Recommendations follow the standard, not the toolchain. If clang < 22 / gcc < 16 haven't shipped a feature, the plugin still suggests the C++26 form. Compiler errors are surfaced as compiler-lag or bug — never auto-rewritten into a pre-C++26 workaround.
The suggestion path (skill + MCP) is compiler-agnostic; compiler awareness lives only in the reviewer's Pass-2 syntax check and the SessionStart probe. Full architecture diagram: docs/architecture.md.
37/39 (95%) with plugin ON vs 14/39 (36%) OFF on a 39-task held suite; bar ≥85%. Per-task scoring + methodology: eval/results-v0.9.0.md, docs/papers.md.
v1.0.0 — eval gate held across two successive refreshes. The MCP tool signatures, the subagent's output schema, and the standard-first invariant are contract-binding for the 1.x line.
Dual-licensed by directory:
- Code (everything outside
corpus/): MIT —LICENSE-CODE. - Knowledge corpus (
corpus/): CC-BY-SA 4.0 —LICENSE-CORPUS.
docs/architecture.md— full invariant, component diagram, walkthroughdocs/examples.md— contracts, senders,#embedside-by-sidedocs/papers.md— the 16 deep-tier papers + eval methodologydocs/FAQ.md— clang/gcc compatibility, legacy code, refresh cadence- Plugin repo: github.com/parasxos/cpp26-adapter · Marketplace: github.com/parasxos/claude-plugins · PyPI: pypi.org/project/cpp26-ref