chromium/base/allocator/partition_allocator/src/partition_alloc/flags.h

// Copyright 2023 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

// This header provides a type-safe way of storing OR-combinations of enum
// values.
//
// The traditional C++ approach for storing OR-combinations of enum values is to
// use an int or unsigned int variable. The inconvenience with this approach is
// that there's no type checking at all; any enum value can be OR'd with any
// other enum value and passed on to a function that takes an int or unsigned
// int.

#ifndef PARTITION_ALLOC_FLAGS_H_
#define PARTITION_ALLOC_FLAGS_H_

#include <type_traits>

namespace partition_alloc::internal {
// Returns `T` if and only if `EnumType` is a scoped enum.
IfEnum;

// We assume `EnumType` defines `kMaxValue` which has the largest value and all
// powers of two are represented in `EnumType`.
kAllFlags;

template <typename EnumType>
constexpr inline IfEnum<EnumType, bool> AreValidFlags(EnumType flags) { … }

// Checks `subset` is a subset of `superset` or not.
template <typename EnumType>
constexpr inline IfEnum<EnumType, bool> ContainsFlags(EnumType superset,
                                                      EnumType subset) { … }

// A macro to define binary arithmetic over `EnumType`.
// Use inside `namespace partition_alloc::internal`.
#define PA_DEFINE_OPERATORS_FOR_FLAGS(EnumType) …

}  // namespace partition_alloc::internal

#endif  // PARTITION_ALLOC_FLAGS_H_