C++ named requirements: UnaryTypeTrait (since C++11)

 

C++

Compiler support

Freestanding and hosted

Language

Standard library

Standard library headers

Named requirements

Feature test macros (C++20)

Language support library

Concepts library (C++20)

Metaprogramming library (C++11)

Diagnostics library

General utilities library

Strings library

Containers library

Iterators library

Ranges library (C++20)

Algorithms library

Numerics library

Localizations library

Input/output library

Filesystem library (C++17)

Regular expressions library (C++11)

Concurrency support library (C++11)

Execution support library (C++26)

Technical specifications

Symbols index

External libraries

 

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)

 

A UnaryTypeTrait is a class template that describes a property of its template type parameter with an std::integral_constant (typically std::bool_constant) specialization.

Requirements

• DefaultConstructible and CopyConstructible.
• Takes one template type parameter (additional template parameters are optional and allowed).
• Publicly and unambiguously derived from a specialization of std::integral_constant, known as its base characteristic.
• The member names of the base characteristic are not hidden and are unambiguously available.

Standard library

The following type traits all satisfy UnaryTypeTrait:

• Primary type categories
• Composite type categories
• Type properties
• Supported operations
• Property queries

The following standard library class templates also satisfy UnaryTypeTrait.

integral_constant (C++11)	compile-time constant of specified type with specified value (class template)
negation (C++17)	logical NOT metafunction (class template)
std::tuple_size<std::tuple> (C++11)	obtains the size of a tuple (class template specialization)
std::tuple_size<std::array> (C++11)	obtains the size of an array (class template specialization)
std::tuple_size<std::pair> (C++11)	obtains the size of a pair (class template specialization)
variant_sizevariant_size_v (C++17)	obtains the size of the variant's list of alternatives at compile time (class template) (variable template)
is_bind_expression (C++11)	indicates that an object is std::bind expression or can be used as one (class template)
is_placeholder (C++11)	indicates that an object is a standard placeholder or can be used as one (class template)
is_execution_policy (C++17)	test whether a class represents an execution policy (class template)