# Appendix A: features and compilers

This appendix lists the C++ features the book uses.
It shows the proposal that introduced or significantly changed each feature.
It also shows the compiler support in the pinned toolchain (Clang 22.1.8, libc++).
The required flag or header is listed.
Finally it indicates whether the book compiles an example or marks it as a gap.

Compiled means the book ships a real example that builds and runs. Gap means the feature is taught prose-first and registered so it builds only with `BOOK_ENABLE_GAPS=ON`. A "Not yet deployable" callout names the supporting compiler if any.

| Feature | Proposal | Clang 22.1.8 | Flag / header | Status |
|---------|----------|--------------|---------------|--------|
| `std::format` / `std::print` / `std::println` | P0645, P2093 | Yes | `<format>`, `<print>`, `-std=c++26` | Compiled |
| `std::mdspan` | P0009 | Yes | `<mdspan>` | Compiled |
| `std::numbers` constants | P0631 | Yes | `<numbers>` | Compiled |
| Concepts | P0734 | Yes | `-std=c++20`+ | Compiled |
| `consteval`, `constinit`, `is_constant_evaluated` | P1073, P1143, P0595 | Yes | `-std=c++20`+ | Compiled |
| Transient `constexpr` allocation | P0784 | Yes | `-std=c++20`+ | Compiled |
| Class-type NTTPs | P0732 | Yes | `-std=c++20`+ | Compiled |
| User-defined literals | C++11 | Yes | `-std=c++20`+ | Compiled |
| `std::generator` | P2502 | Yes | `<generator>` | Compiled |
| `std::jthread` / stop tokens | P0660 | Yes | `<thread>`, `<stop_token>` | Compiled |
| `std::atomic_ref` | P0019 | Yes | `<atomic>` | Compiled |
| `std::scoped_lock` | P0156 | Yes | `<mutex>` | Compiled |
| `std::ranges` / views | P0896, P2325 | Yes | `<ranges>`, `<algorithm>` | Compiled |
| `std::execution::par` | P0024 | No | `<execution>` | Prose only |
| Contracts (`[[assert]]`, `[[expects]]`, `[[ensures]]`) | P2900 | No (GCC 16) | `-fcontracts` | Gap |
| `std::execution` (P2300 senders) | P2300 | No | `<execution>` | Gap |
| `std::linalg` | P1673 | No | `<linalg>` | Gap |
| Static reflection | P2996 | No (GCC 16 partial) | `<experimental/meta>` | Gap |
| `<hazard_pointer>` / `<rcu>` | P2530, P2546 | No | `<hazard_pointer>`, `<rcu>` | Gap |
| Modules (`import`, `export module`) | P1103 | Partial | `-std=c++26`, BMI | Gap |
| Lifetime-safety analysis | P1179 | Experimental | `-Xclang -fexperimental-lifetime-safety` | Compiled (demos) |

The Nix dev shell in `flake.nix` provides the pinned toolchain. The book compiles only verified examples. Newer features are taught with exact syntax and an honest callout.