src/utils/underlying_type.h

// Copyright 2020 The Dawn & Tint Authors
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#ifndef SRC_UTILS_UNDERLYING_TYPE_H_
#define SRC_UTILS_UNDERLYING_TYPE_H_

#include <concepts>
#include <type_traits>

namespace dawn {

// UnderlyingType is similar to std::underlying_type_t. It is a passthrough for already
// integer types which simplifies getting the underlying primitive type for an arbitrary
// template parameter. It includes a specialization for detail::TypedIntegerImpl which yields
// the wrapped integer type.
namespace detail {
template <typename T, typename Enable = void>
struct UnderlyingTypeImpl;

template <typename I>
    requires std::integral<I>
struct UnderlyingTypeImpl<I> {
    using type = I;
};

template <typename E>
    requires std::is_enum_v<E>
struct UnderlyingTypeImpl<E> {
    using type = std::underlying_type_t<E>;
};

// Forward declare the TypedInteger impl.
template <typename Tag, typename T>
class TypedIntegerImpl;

template <typename Tag, typename I>
struct UnderlyingTypeImpl<TypedIntegerImpl<Tag, I>> {
    using type = typename UnderlyingTypeImpl<I>::type;
};
}  // namespace detail

template <typename T>
using UnderlyingType = typename detail::UnderlyingTypeImpl<T>::type;

template <typename T>
concept HasUnderlyingType = std::integral<UnderlyingType<T>>;

template <typename T>
concept HasUnsignedUnderlyingType = std::unsigned_integral<UnderlyingType<T>>;

}  // namespace dawn

#endif  // SRC_UTILS_UNDERLYING_TYPE_H_