C++ named requirements: UnaryTypeTrait

 

C++

Language

Standard Library Headers

Freestanding and hosted implementations

Named requirements

Language support library

Concepts library (C++20)

Diagnostics library

Utilities library

Strings library

Containers library

Iterators library

Ranges library (C++20)

Algorithms library

Numerics library

Input/output library

Localizations library

Regular expressions library (C++11)

Atomic operations library (C++11)

Thread support library (C++11)

Filesystem library (C++17)

Technical Specifications

 

C++ named requirements

Basic
DefaultConstructible CopyAssignable CopyConstructible	MoveAssignable (C++11) MoveConstructible (C++11) Destructible
Layout
TrivialType (C++11) TriviallyCopyable (C++11)	StandardLayoutType (C++11) PODType
Library-Wide
EqualityComparable LessThanComparable Swappable (C++11) ValueSwappable (C++11) NullablePointer (C++11) Hash (C++11)	Allocator FunctionObject Callable Predicate BinaryPredicate Compare
Container
Container SequenceContainer ContiguousContainer (C++17) ReversibleContainer	AssociativeContainer AllocatorAwareContainer UnorderedAssociativeContainer (C++11)
Container Elements
DefaultInsertable (C++11) CopyInsertable (C++11) MoveInsertable (C++11)	EmplaceConstructible (C++11) Erasable (C++11)
Iterator
LegacyIterator LegacyOutputIterator LegacyInputIterator LegacyForwardIterator	LegacyBidirectionalIterator LegacyRandomAccessIterator LegacyContiguousIterator (C++17) ConstexprIterator (C++20)
Stream I/O
FormattedInputFunction UnformattedInputFunction	FormattedOutputFunction UnformattedOutputFunction
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)	Mutex (C++11) TimedMutex (C++11) SharedMutex (C++17) SharedTimedMutex (C++14)
Other
CharTraits RegexTraits (C++11) BitmaskType NumericType LiteralType (C++11)	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 a intergral_constant (typically 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 intergral_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 properties 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)
tuple_size	obtains the size of tuple at compile time (class template specialization)
std::tuple_size<std::array>	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)