C++17. Targets GCC & Clang (MSVC is WIP). Namespace
ltl.
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ltl::is_scoped_enum<T>; // Test if type T is a scoped enum (lazy).
ltl::is_scoped_enum_v<T>; // Test if type T is a scoped enum (eager).
ltl::is_fixed_enum<T>; // Test if type T is a 'fixed' enum,
ltl::is_fixed_enum_v<T>; // i.e. an enum with fixed underlying type.
ltl::underlying_type<T>; // c++17 port of c++20's improved UB-free
ltl::underlying_type_t<T>; // 'SFINAE-friendly' std::underlying_type.
ltl::to_underlying(e); // Convenience cast to underlying type P1682.C++17. Targets GCC>=9 and Clang (recent MSVC possible). Namespace
ltl.
Copyright © 2019 Will Wray. Distributed under LGPL-3.0-or-later.
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ltl::is_enumerated_v<e>; // Test if enum value e corresponds to an
// enumerator of its enum type decltype(e).
ltl::enumerators_v<E>; // Array of enumerated values of enum type E
// (see note on duplicate-valued enumerators).
ltl::enumerators_t<E>; // integer_sequence<underlying_type_t<E>,u...>
// of E's enumerators' underlying values u...
ltl::enumerators<E>; // Trait class for enumerated values of E with
// array 'value' and typedef 'type' members.The array returned by enumerators_v is of an internal type, sufficient
to index,
range-for iterate or copy into another container.
Two header-only libraries of 'type traits'; template-based utilities to query:
enum_traitsProperties of enum typesenumerator_traitsEnumerated values of an enum type
The traits interface is constexpr; runtime facilities can be built on top.
These libraries deal only with enumerated values, not with names of ids.
Reflection of names can be dealt with at a higher level.
See the example repo for full reflection of enum types, including names.
A 'brute force' method is used to check possible values of the underlying type.
It takes around a second to exhaustively check all 2^16 values of a 16-bit enum
(on a decent recent dev box - GCC faster than Clang, MSVC out of the game).
Enum types with <= 16-bit underlying type are fully supported - exhaustive check
Enum types with 32-bit underlying type are partially supported - far from exhaustive.
2^16 values of the same-signed 16-bit integer are checked, plus:
- for uint32, check 392 high values (
UINT16_MAX,UINT32_MAX]. - for int32, check 32 negative values [
INT32_MIN,INT16_MIN)- and 360 high positive values (
INT16_MAX,INT32_MAX].
- and 360 high positive values (
The 32-bit Int_MAX high ranges comprise all values with a contiguous run of set bits.
This means that 'flag enums' with contiguous bitfield / bitmask values are supported.
Enum types with 64-bit underlying type are unsupported, giving a compile error.
GCC>=9 is required for a bugfix (earlier versions can be patched).
MSVC is work in progress. 8-bit underlying value works.
C++17 for auto template parameters, constexpr if, inline variables...
Enumerator extraction uses non-standard 'pretty function' preprocessor
extensions whose output differs between compilers & compiler versions.
This is not a future-proof solution. Use with caution.
Test for your use-case and target platforms.
Meson build script provided, e.g. use with ninja backend
meson build
ninja -C build| Linux Travis | Windows Appveyor |
|---|---|
| gcc-9, clang-7 -std=c++17 |
MSVC 19.21.27702.2 /std:c++latest |
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