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Use bitwise OR for magic_enum::enum_fuse (#131)

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Pavel I. Kryukov 2022-02-11 19:35:50 +03:00 • committed by GitHub
parent e7b9231906
commit 5444f00a04
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2 changed files with 36 additions and 24 deletions
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2
doc/reference.md
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@ -333,7 +333,7 @@ template <typename... Es>
[[nodiscard]] constexpr std::size_t enum_fuse(Es... values);
```
* Returns a bijective mix of several enum values with [Cantor pairing function](https://en.wikipedia.org/wiki/Pairing_function). This can be used to emulate 2D switch/case statements.
* Returns a bijective mix of several enum values. This can be used to emulate 2D switch/case statements.
* Examples

58
include/magic_enum.hpp
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@ -324,15 +324,6 @@ constexpr I log2(I value) noexcept {
return ret;
}
constexpr std::size_t cantor_pair(size_t v1, size_t v2) noexcept {
return (((v1 + v2) * (v1 + v2 + 1)) >> 1) + v2;
}
template <typename... Ts>
constexpr std::size_t cantor_pair(std::size_t v1, std::size_t head, Ts... tail) noexcept {
return cantor_pair(cantor_pair(v1, head), tail...);
}
template <typename T>
inline constexpr bool is_enum_v = std::is_enum_v<T> && std::is_same_v<T, std::decay_t<T>>;
@ -887,20 +878,6 @@ template <typename E>
return {}; // Invalid value or out of range.
}
// Returns a bijective mix of several enum values with [Cantor pairing function](https://en.wikipedia.org/wiki/Pairing_function). This can be used to emulate 2D switch/case statements.
template <typename... Es>
[[nodiscard]] constexpr auto enum_fuse(Es... values) -> std::enable_if_t<(std::is_enum_v<std::decay_t<Es>> && ...), std::size_t>{
static_assert(sizeof...(Es) >= 2, "magic_enum::enum_fuse requires at least 2 enums");
const bool has_values = (enum_index(values).has_value() && ...);
#if defined(__cpp_lib_is_constant_evaluated) && (defined(__cpp_exceptions) || defined(__EXCEPTIONS) || (defined(_HAS_EXCEPTIONS) && _HAS_EXCEPTIONS))
if (std::is_constant_evaluated() && !has_values) {
throw std::logic_error{"magic_enum::enum_fuse accepts only in-range enum values"};
}
#endif
// Add 1 to prevent matching 2D fusions with 3D fusions etc.
return assert(has_values), (has_values ? detail::cantor_pair((enum_index(values).value() + 1)...) : 0);
}
// Checks whether enum contains enumerator with such enum value.
template <typename E>
[[nodiscard]] constexpr auto enum_contains(E value) noexcept -> detail::enable_if_enum_t<E, bool> {
@ -930,6 +907,41 @@ template <typename E>
return enum_cast<std::decay_t<E>>(value).has_value();
}
namespace fusion_detail {
template<typename E>
constexpr std::size_t fuse_one_enum(std::size_t hash, E value) noexcept {
// Add 1 to prevent matching 2D fusions with 3D fusions etc.
std::size_t index = enum_index(value).has_value() ? enum_index(value).value() + 1 : 0;
return (hash << detail::log2(enum_count<E>() + 1)) | index;
}
template <typename E>
constexpr std::size_t fuse_enum(E value) noexcept {
return fuse_one_enum(0, value);
}
template <typename E, typename ... Es>
constexpr std::size_t fuse_enum(E head, Es ... tail) noexcept {
return fuse_one_enum(fuse_enum(tail...), head);
}
} // namespace magic_enum::fusion_detail
// Returns a bijective mix of several enum values. This can be used to emulate 2D switch/case statements.
template <typename... Es>
[[nodiscard]] constexpr auto enum_fuse(Es... values) -> std::enable_if_t<(std::is_enum_v<std::decay_t<Es>> && ...), std::size_t>{
static_assert(sizeof...(Es) >= 2, "magic_enum::enum_fuse requires at least 2 enums");
static_assert((detail::log2(enum_count<Es>() + 1) + ...) <= sizeof(std::size_t) * 8, "magic_enum::enum_fuse does not work for long enums");
const bool has_values = (enum_index(values).has_value() && ...);
#if defined(__cpp_lib_is_constant_evaluated) && (defined(__cpp_exceptions) || defined(__EXCEPTIONS) || (defined(_HAS_EXCEPTIONS) && _HAS_EXCEPTIONS))
if (std::is_constant_evaluated() && !has_values) {
throw std::logic_error{"magic_enum::enum_fuse accepts only in-range enum values"};
}
#endif
return assert(has_values), (has_values ? fusion_detail::fuse_enum(values...) : 0);
}
namespace ostream_operators {
template <typename Char, typename Traits, typename E, detail::enable_if_enum_t<E, int> = 0>