C++23 evaluation

Assessment date: 2026-09-13.

C++23 mode is supported; C++20 remains the default and minimum. Full C++23 framework tests have passed locally on macOS and in Ubuntu Clang CI. Adopt individual newer facilities only when they solve a demonstrated problem across the supported toolchains. Changing the language flag alone does not repair ownership, cancellation, collection diffs, or reentrancy, and does not establish a performance improvement.

Benefits for Aria

Facility	Potential use	Decision
std::expected<T, Error>	Explicit success/failure for new synchronous APIs	Useful when such an API is needed. Existing Loadable<T> also represents idle, loading, refreshing, and stale data; it cannot be replaced by a two-state result.
std::move_only_function	Owning callbacks with move-only captures	Useful, but unavailable in the tested Apple and Android standard libraries. It also does not provide the fixed-capacity, no-heap contract of inplace_function.
std::generator	Standardize the synchronous generator	Cannot currently replace Aria's generator on all target toolchains. It does not replace asynchronous Task, executors, or cancellation.
Explicit object parameters (deducing this)	Reduce some const/ref overload duplication	A modest maintenance benefit; it would raise the compiler floor for public headers.
std::to_underlying, optional monadic operations, range helpers	Shorter implementation code	Small local improvements; insufficient reason to raise every consumer's minimum standard.

Aria's function_ref has a separate non-owning contract. Its standard-library counterpart is a C++26 facility, so C++23 alone does not remove that component.

Local compiler and linker probes

Each cell below was tested with a small translation unit that actually uses the facility and links an executable. These are feature probes, not a claim that every Aria test has run on every operating-system version.

Toolchain / target	expected and transform	to_underlying	Explicit object parameters	move_only_function	generator
Apple Clang 21 / macOS arm64	Pass	Pass	Pass	Unavailable	Unavailable
Apple Clang 21 / iOS simulator arm64, minimum iOS 15	Pass	Pass	Pass	Unavailable	Unavailable
Android NDK r29, Clang 21 / arm64, API 21	Pass	Pass	Pass	Unavailable	Unavailable
Android NDK r25b, Clang 14 / arm64, API 21	Unavailable	Unavailable	Unavailable	Unavailable	Unavailable

The newer toolchains used -std=c++23; r25b used its accepted spelling -std=c++2b. Failure is the absence of the tested facility, not a claim that the compiler rejects every C++23 program.

Apple distinguishes compiler support from facilities requiring the deployed OS's libc++.dylib; each adopted feature needs a deployment-target check. For example, its support table requires Xcode 16.3 for explicit object parameters. Apple C++ support

NDK r29 updates the LLVM toolchain to clang-r563880c. Its exact standard-library feature set must still be probed; the release number is not a promise of full C++23 conformance. NDK r29 changelog

Windows and Linux

GCC's library provides expected and move_only_function from GCC 12.1, and expected monadic operations from 13.1. Aria's GCC 13 CI therefore has these facilities, but this does not establish availability in Clang's selected library: Linux Clang can use either libstdc++ or libc++. libstdc++ feature status

MSVC documents support per compiler and library feature, rather than treating the standard as an indivisible capability. A Windows C++23 build must pin a toolset and its supported /std mode, then run the framework and adapter tests. MSVC conformance table

LLVM's current status table still lists gaps, including std::generator. The Apple/NDK probe results above are therefore decisive for the facilities Aria could otherwise replace. libc++ C++23 status

Adoption policy

1. Preserve exported cxx_std_20 requirements and the default C++20 build. Respect an explicit parent-project or command-line CMAKE_CXX_STANDARD=23.
2. Test C++20 and C++23 builds without conditionally changing public type layouts or exported signatures. Consumers of one binary must agree on its ABI, regardless of their language mode.
3. Evaluate each candidate with feature-test macros and compile/link/runtime probes for Windows, Linux, Android, and Apple deployment targets.
4. Raise the minimum only when a measured simplification, required feature, or performance improvement outweighs the consumer toolchain upgrade. Document any API/ABI migration as a release-level change.

No C++23-only public API or baseline migration is part of this assessment.