A C++20 library for using bitwise operators on flag enums

This library provides a set of free function templates which perform bitwise operations on scoped enums that satisfy the Flag concept. When these function templates are used, instead of return int like normal bitwise operators, they return the underlying type of the input enum.

Examples

#include <cassert>
#include <cstdint>
#include <river/flag.hpp>

namespace filesystem {
enum class FilePermission : std::uint16_t {
  all_execute = 0b0'000'000'001,
  all_write   = 0b0'000'000'010,
  all_read    = 0b0'000'000'100,

  group_execute = 0b0'000'001'000,
  group_write   = 0b0'000'010'000,
  group_read    = 0b0'000'100'000,

  user_execute = 0b0'001'000'000,
  user_write   = 0b0'010'000'000,
  user_read    = 0b0'100'000'000,

  directory = 0b1'000'000'000
};
IS_FLAG_ENUM(FilePermission); // Opting in making FilePermission enum as a flag enum
} // namespace filesystem

int main() {
  using namespace river::flags; // All operators are define in the river namespace
  using filesystem::FilePermission;

  // type of file_permission is std::uint16_t
  auto file_permission = FilePermission::all_execute | FilePermission::user_execute;

  assert(has<FilePermission::all_execute>(file_permission));
  assert(has<FilePermission::user_execute>(file_permission));

  // Add group_execute to file_permission
  file_permission |= FilePermission::group_execute;
  assert(has<FilePermission::group_execute>(file_permission));

  // Toggle user_execute bit of file_permission
  file_permission ^= FilePermission::user_execute;
  assert(!has<FilePermission::user_execute>(file_permission));
  file_permission ^= FilePermission::user_execute;
  assert(has<FilePermission::user_execute>(file_permission));
}

Usage

This is a header only library, copy the file flag.hpp to your source code and start using it.

Users can mark their scoped enums as flag enums by using the macro IS_FLAG_ENUM with the parameter as the name of the enum (qualified if used out of the scope that the enum is defined).