forked from mirrors/gecko-dev
113 lines
3.4 KiB
C++
113 lines
3.4 KiB
C++
/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
|
|
/* This Source Code Form is subject to the terms of the Mozilla Public
|
|
* License, v. 2.0. If a copy of the MPL was not distributed with this
|
|
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
|
|
|
|
/* Type traits for enums. */
|
|
|
|
#ifndef mozilla_EnumTypeTraits_h
|
|
#define mozilla_EnumTypeTraits_h
|
|
|
|
#include <stddef.h>
|
|
#include <type_traits>
|
|
|
|
namespace mozilla {
|
|
|
|
namespace detail {
|
|
|
|
template <size_t EnumSize, bool EnumSigned, size_t StorageSize,
|
|
bool StorageSigned>
|
|
struct EnumFitsWithinHelper;
|
|
|
|
// Signed enum, signed storage.
|
|
template <size_t EnumSize, size_t StorageSize>
|
|
struct EnumFitsWithinHelper<EnumSize, true, StorageSize, true>
|
|
: public std::integral_constant<bool, (EnumSize <= StorageSize)> {};
|
|
|
|
// Signed enum, unsigned storage.
|
|
template <size_t EnumSize, size_t StorageSize>
|
|
struct EnumFitsWithinHelper<EnumSize, true, StorageSize, false>
|
|
: public std::integral_constant<bool, false> {};
|
|
|
|
// Unsigned enum, signed storage.
|
|
template <size_t EnumSize, size_t StorageSize>
|
|
struct EnumFitsWithinHelper<EnumSize, false, StorageSize, true>
|
|
: public std::integral_constant<bool, (EnumSize * 2 <= StorageSize)> {};
|
|
|
|
// Unsigned enum, unsigned storage.
|
|
template <size_t EnumSize, size_t StorageSize>
|
|
struct EnumFitsWithinHelper<EnumSize, false, StorageSize, false>
|
|
: public std::integral_constant<bool, (EnumSize <= StorageSize)> {};
|
|
|
|
} // namespace detail
|
|
|
|
/*
|
|
* Type trait that determines whether the enum type T can fit within the
|
|
* integral type Storage without data loss. This trait should be used with
|
|
* caution with an enum type whose underlying type has not been explicitly
|
|
* specified: for such enums, the C++ implementation is free to choose a type
|
|
* no smaller than int whose range encompasses all possible values of the enum.
|
|
* So for an enum with only small non-negative values, the underlying type may
|
|
* be either int or unsigned int, depending on the whims of the implementation.
|
|
*/
|
|
template <typename T, typename Storage>
|
|
struct EnumTypeFitsWithin
|
|
: public detail::EnumFitsWithinHelper<
|
|
sizeof(T),
|
|
std::is_signed<typename std::underlying_type<T>::type>::value,
|
|
sizeof(Storage), std::is_signed<Storage>::value> {
|
|
static_assert(std::is_enum<T>::value, "must provide an enum type");
|
|
static_assert(std::is_integral<Storage>::value,
|
|
"must provide an integral type");
|
|
};
|
|
|
|
/*
|
|
* Provides information about highest enum member value.
|
|
* Each specialization of struct MaxEnumValue should define
|
|
* "static constexpr unsigned int value".
|
|
*
|
|
* example:
|
|
*
|
|
* enum ExampleEnum
|
|
* {
|
|
* CAT = 0,
|
|
* DOG,
|
|
* HAMSTER
|
|
* };
|
|
*
|
|
* template <>
|
|
* struct MaxEnumValue<ExampleEnum>
|
|
* {
|
|
* static constexpr unsigned int value = static_cast<unsigned int>(HAMSTER);
|
|
* };
|
|
*/
|
|
template <typename T>
|
|
struct MaxEnumValue; // no need to define the primary template
|
|
|
|
/**
|
|
* Get the underlying value of an enum, but typesafe.
|
|
*
|
|
* example:
|
|
*
|
|
* enum class Pet : int16_t {
|
|
* Cat,
|
|
* Dog,
|
|
* Fish
|
|
* };
|
|
* enum class Plant {
|
|
* Flower,
|
|
* Tree,
|
|
* Vine
|
|
* };
|
|
* UnderlyingValue(Pet::Fish) -> int16_t(2)
|
|
* UnderlyingValue(Plant::Tree) -> int(1)
|
|
*/
|
|
template <typename T>
|
|
inline constexpr auto UnderlyingValue(const T v) {
|
|
static_assert(std::is_enum_v<T>);
|
|
return static_cast<typename std::underlying_type<T>::type>(v);
|
|
}
|
|
|
|
} // namespace mozilla
|
|
|
|
#endif /* mozilla_EnumTypeTraits_h */
|