d2mcpp-authoring

d2mcpp (D2X) Authoring Conventions

d2mcpp teaches Modern C++ core language features through a tightly coupled quartet: Book (mdBook) + Code (dslings exercises) + Solution + Auto-checker (d2x checker), all of it bilingual (zh + en). A "lesson" is never one file — it is a coordinated set across several directories. The cardinal sin here is producing a half-set (a chapter with no exercise, a zh file with no en counterpart, an exercise not registered in xmake). This skill exists so every lesson lands complete and consistent.

Read references/anatomy.md for the full directory map and the exact list of files every lesson must touch. Use the ready-made scaffolds in assets/ rather than reconstructing format from memory.

The design principle (decide this BEFORE writing)

The project is organized by standard (cpp11/ cpp14/ cpp17/ cpp20/ cpp23/). Honor that axis:

• Teach each feature as the standard that introduced it actually delivered it — the historical state, compiled at its introduction standard. The compiler-driven (dslings) format is at its best when the learner feels the C++11-era restriction first (e.g. constexpr single-return, std::is_pod, copy-elision behavior). Folding every later refinement back into the introduction chapter erases that, and empties out the later-standard sections.
• Independent later capabilities become their own chapter under the later standard's section — this is what fills cpp14/17/20. Examples: fold expressions → cpp17, using enum → cpp20, designated initializers → cpp20, if constexpr → cpp17, decltype(auto) → cpp14, consteval/constinit → cpp20.
• Pure refinements / rule-tweaks / deprecations stay in the introduction chapter as a short "特性演进 / Feature Evolution" note with a cross-link forward — they are not chapter-worthy on their own. Examples: auto x{1} deduction change, std::is_pod deprecation pointer, guaranteed copy elision remark, P0136 inheriting-constructor semantics fix.
• Compile each chapter at its introduction standard. Do not globally pin a newer standard. If one exercise genuinely needs a later standard, make it an explicit, commented exception in xmake — never a bare -- TODO hack.

Background and the full per-feature evolution analysis live in .agents/docs/2026-06-08-cpp11-feature-evolution-and-cxx20-baseline.md. Consult it when deciding where a feature's later improvements should go.

The decision rule, compactly:

The unit of work: one lesson = these files, all bilingual

When adding a feature numbered NN with slug topic (e.g. 06-scoped-enums):

1. book/src/<std>/NN-topic.md — zh chapter
2. book/en/src/<std>/NN-topic.md — en chapter (translate prose, keep code identical)
3. dslings/<std>/NN-topic-K.cpp — one or more exercises (K = 0,1,2…), zh comments
4. dslings/en/<std>/NN-topic-K.cpp — en exercises (translate comments only)
5. solutions/<std>/NN-topic-K.cpp — reference solution per exercise
6. Register each exercise target in dslings/<std>/xmake.lua
7. Register each solution target in solutions/xmake.lua
8. Add the chapter line to both book/src/SUMMARY.md and book/en/src/SUMMARY.md
9. Add a changelog entry to both book/src/changelog.md and book/en/src/changelog.md

Missing any of these = an incomplete lesson. references/anatomy.md has the exact registration snippets and SUMMARY/changelog line formats.

Naming and numbering

• Chapter/exercise prefix is a two-digit sequence NN within the standard section; slug is kebab-case and matches book + dslings + solutions.
• Exercises split into -0, -1, … by sub-topic; a single-exercise chapter has no numeric suffix on the dslings target name but the file is still NN-topic.cpp.
• The d2x checker <name> name is the slug (and <slug>-1, <slug>-2 for later exercises) — it omits the NN- prefix. Keep checker names, file names, and book references mutually consistent.

Book chapter format

Use assets/chapter.zh.md / assets/chapter.en.md. Required structure, in order:

1. Language-switch header <div align=right> 🌎 [中文] | [English] + link defs.
   • zh links: [中文]: ./NN-topic.html and [English]: ../en/<std>/NN-topic.html
   • en links: [中文]: ../../<std>/NN-topic.html and [English]: ./NN-topic.html
2. # 标题 - english name (zh) / # English Title (en), then a one-paragraph intro that states the feature was introduced in C++NN and what problem it solves.
3. Resource table | Book | Video | Code | X | — cppreference link + markdown permalink + video link + first practice-code permalink.
4. Bold motivation blocks: **为什么引入?**, **和……的区别?**.
5. Numbered Chinese-numeral sections, in order: ## 一、基础用法和场景, ## 二、真实案例 - STL 中的 <feature>, ## 三、注意事项, ## 四、练习代码, ## 五、其他.
6. ## 二、真实案例 corroborates the feature with real, verbatim STL code quoted from the in-repo msvc-stl/ basis — see "The 真实案例 section" below.
7. ## 四、练习代码 lists every exercise topic of the chapter (-0, -1, …, matching the dslings/xmake count) with dslings links as an index, but the checker block shows only the single entry command d2x checker <name> — d2x auto- advances through the remaining exercises, so do NOT list one command per exercise. Then a ### 练习交流讨论 link to the chapter's forum thread. Each exercise's own d2x checker <name>-K name and a Tips line specific to that exercise belong in that exercise file's header, not in the book.
8. ## 五、其他 is the fixed footer (forum / repo / video list / xlings links).
9. If the feature evolved later, add a ## 特性演进 / Feature Evolution block before ## 五、其他 — introduced standard + bullet list of later refinements + forward links to the later-standard chapters.

Keep prose tone consistent with existing chapters: explanatory, example-driven, short code blocks with inline comments showing the failure and the fix.

The 真实案例 / Real-World Case section (msvc-stl basis)

## 二、真实案例 exists to prove the feature earns its place by showing real production code, quoted verbatim — never invented, never paraphrased. The single source of truth is the in-repo vendored MSVC STL basis at the top-level msvc-stl/ (the complete upstream stl/ subtree; msvc-stl/SOURCE.md records the pinned upstream commit and how to refresh it). Rules:

• Quote from msvc-stl/stl/inc/<header> (or src/) byte-for-byte; mark any elision with (有删节) / (abridged). Do not reconstruct from memory.
• Keep internal macros (_NODISCARD, _CONSTEXPR17, _STD, …) as written and add one line telling the reader they are library-internal and ignorable.
• Pick a usage that echoes a syntax point from ## 一 (e.g. std::begin's auto … -> decltype(...) for the auto/decltype chapter), so the section reads as "you use it this way → the standard library does too".
• Scope-lock to the chapter's standard: a cpp11 chapter quotes C++11-era usage only; do not show later forms (e.g. decltype(auto)).
• Link to the local msvc-stl/ path, not the upstream GitHub repo, so the citation stays pinned to the vendored snapshot.
• Every chapter should carry this section. If a feature genuinely has no representative usage in the STL implementation, omit it and state why in the PR.

dslings exercise format

Use assets/exercise.cpp. Essentials:

• Header comment block: d2mcpp URL, license: Apache-2.0, file: path, Exercise/练习: line (<std> | NN - topic | 中文小标题), Tips/提示:, Docs/文档: (cppreference), and the Auto-Checker/自动检测命令: with d2x checker <name>.
• #include <d2x/cpp/common.hpp> then any std headers.
• main() seeded with intentional errors the learner fixes, each flagged by a numbered inline comment (// 1.…, // 2.…) telling them what to do.
• Checkpoint macros from d2x/cpp/common.hpp:
  • d2x_assert(cond) / d2x_assert_eq(a, b) — runtime checkpoints; learners must make them pass by fixing code, not by deleting the checkpoint.
  • D2X_YOUR_ANSWER — a fill-in placeholder the learner replaces.
  • D2X_WAIT — separates exercises; learner deletes/comments it to advance. Put exactly one at the end of each exercise's checkpoints.
  • D2X_DONT_DELETE_THIS — guards lines that must not be removed.
• The en exercise translates only the comment prose; the code stays byte-for-byte identical to the zh exercise so checker behavior matches.

Reference solution format

Use assets/solution.cpp. It is the corrected exercise with:

• A solution header: reference solution for: <exercise path>, plus the note that it is for CI/maintainers only, not a tutorial entry, and a pointer back to the exercise file.
• D2X_WAIT removed; all checkpoints passing; unused locals silenced with (void)var; rather than left to warn.
• Same #includes and structure as the exercise.

Definition of done

Before claiming a lesson complete, verify the whole set exists and is wired up, and that the exercise/solution actually build & check. See references/anatomy.md for the verification commands (d2x checker <name> and the xmake build) — run them; do not assert success without the output.