C++ named requirements: BitmaskType

 

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C++ named requirements

Basic DefaultConstructible MoveConstructible (C++11) CopyConstructible CopyAssignable MoveAssignable (C++11) Destructible Type properties ScalarType PODType TriviallyCopyable (C++11) TrivialType (C++11) StandardLayoutType (C++11)   ImplicitLifetimeType Library-wide BooleanTestable EqualityComparable LessThanComparable Swappable ValueSwappable (C++11) NullablePointer (C++11) Hash (C++11) Allocator FunctionObject Callable Predicate BinaryPredicate Compare

Container Container ReversibleContainer AllocatorAwareContainer SequenceContainer ContiguousContainer (C++17) AssociativeContainer UnorderedAssociativeContainer (C++11)   Container element DefaultInsertable (C++11) CopyInsertable (C++11) MoveInsertable (C++11) EmplaceConstructible (C++11) Erasable (C++11) Iterator LegacyIterator LegacyInputIterator LegacyOutputIterator LegacyForwardIterator LegacyBidirectionalIterator LegacyRandomAccessIterator LegacyContiguousIterator (C++17) ConstexprIterator (C++20) Stream I/O FormattedInputFunction UnformattedInputFunction FormattedOutputFunction UnformattedOutputFunction Formatters BasicFormatter (C++20) Formatter (C++20)

Random Numbers SeedSequence (C++11) RandomNumberEngine (C++11) RandomNumberDistribution (C++11) UniformRandomBitGenerator (C++11) RandomNumberEngineAdaptor (C++11) Concurrency BasicLockable (C++11) Lockable (C++11) TimedLockable (C++11) SharedLockable (C++14) SharedTimedLockable (C++14) Mutex (C++11) TimedMutex (C++11) SharedMutex (C++17) SharedTimedMutex (C++14) Ranges RangeAdaptorObject (C++20) RangeAdaptorClosureObject (C++20) Multidimensional View LayoutMapping (C++23) LayoutMappingPolicy (C++23) AccessorPolicy (C++23) Other CharTraits RegexTraits (C++11)   BitmaskType LiteralType (C++11) NumericType UnaryTypeTrait (C++11) BinaryTypeTrait (C++11) TransformationTrait (C++11) Clock (C++11) TrivialClock (C++11)

 

Defines a type that can be used to represent a set of constant values or any combination of those values. This trait is typically implemented by integer types, std::bitset, or enumerations (scoped and unscoped) with additional operator overloads.

Requirements

The bitmask type supports a finite number of bitmask elements, which are distinct non-zero values of the bitmask type, such that, for any pair Ci and Cj, Ci & Ci is nonzero and Ci & Cj is zero. In addition, the value 0 is used to represent an empty bitmask, with no values set.

The bitwise operators operator&, operator|, operator^, operator~, operator&=, operator|=, and operator^= are defined for values of the bitmask type and have the same semantics as the corresponding built-in operators on unsigned integers would have if the bitmask elements were the distinct integer powers of two.

The following expressions are well-formed and have the following meaning for any BitmaskType:

X |= Y	sets the value Y in the object X
X &= ~Y	clears the value Y in the object X
X & Y	nonzero result indicates that the value Y is set in the object X

Each representable bitmask element is defined as a inline(since C++17)constexpr value of the bitmask type.

Usage

The following standard library types satisfy BitmaskType:

• std::ctype_base::mask
• std::ios_base::fmtflags
• std::ios_base::iostate
• std::ios_base::openmode
• std::regex_traits::char_class_type (since C++11)
• std::regex_constants::syntax_option_type (since C++11)
• std::regex_constants::match_flag_type (since C++11)
• std::launch (since C++11)
• std::filesystem::perms (since C++17)
• std::filesystem::copy_options (since C++17)
• std::filesystem::directory_options (since C++17)

Code that relies on some particular implementation option (e.g. int n = std::ios_base::hex), is nonportable because std::ios_base::fmtflags is not necessarily implicitly convertible to int.