C++20 on Symbian

Use C++20 with the SDK's Clang ARM toolchain and matching guest runtime. ARMv5T and ARMv6 use AAPCS soft-float and 16-bit wchar_t. Language features and standard-library facilities have separate requirements: see Clang language support, libc++ library support, and the guest runtime for the SDK's available library profiles.

Concepts, constrained lambdas, consteval, designated initialization, structural template arguments, defaulted equality, char8_t and [[no_unique_address]] are available. Runtime allocation, global initialization and concurrency use the SDK implementations rather than host libraries. Exceptions and RTTI are disabled by default. General C++ TLS, thread-safe local-static initialization, import std, and header units are unsupported.

A small language example

For a thumbnail layout, designated initialization names each coordinate and defaulted equality makes detecting an unchanged position straightforward:

struct GridPosition {
  int column;
  int row;
  bool operator==(const GridPosition&) const = default;
};

GridPosition ThumbnailPosition(unsigned index) {
  return {.column = static_cast<int>(index % 3),
          .row = static_cast<int>(index / 3)};
}

This three-column layout assumes the caller has bounded index to its item count and a representable row. Neither feature allocates or calls an OS service.

From a source checkout:

symbian build --project probes/cxx20_probe \
  --output .symbian/cxx20-probe
symbian package --project probes/cxx20_probe \
  --artifact .symbian/cxx20-probe/cxx20_probe.exe \
  --output .symbian/cxx20-package
symbian inspect --format e32 .symbian/cxx20-probe/cxx20_probe.exe

This runnable diagnostic probe uses no system C/C++ headers, allocation, exceptions or RTTI. Its startup exits directly and owns no target resources. Use generated application startup when your program needs the guest runtime or OS handles.

Named modules

Install upstream Clang with matching clang-scan-deps, CMake 3.28+ and Ninja 1.12+. Put the LLVM tools on PATH and build the module example:

symbian build --project probes/cxx20_module_probe \
  --compiler "$(command -v clang++)" \
  --output .symbian/cxx20-module
symbian package --project probes/cxx20_module_probe \
  --artifact .symbian/cxx20-module/cxx20_module_probe.exe \
  --output .symbian/cxx20-module-package

The module diagnostic probe uses a CXX_MODULES file set and enables scanning for its target. CMake/Ninja discovers imported BMIs and retains them in the build tree; ordinary SDK targets leave scanning off. See CMake's module rules. Module symbols link within the executable; exporting a module name does not create an interface to a historical Symbian DLL.

Standard-library configuration

Use the installed SDK's headers and its selected runtime archive together. A host libc++ configuration can enable platform services absent on Symbian, and a header-only overlay cannot supply those services. The SDK generates its own target configuration following LLVM's vendor guidance.

Symbian::Runtime supplies the core library; Symbian::Streams adds classic locale and string-stream support. Abseil-based SDK components select the matching streams profile. Do not link both runtime archives into one image. For asynchronous code, use the SDK concurrency APIs.