C++ named requirements: RangeAdaptorObject (since C++20)

 

C++

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C++ named requirements

Basic
DefaultConstructible CopyAssignable	CopyConstructible MoveAssignable (C++11)	MoveConstructible (C++11) Destructible
Type properties
ScalarType TriviallyCopyable (C++11)	StandardLayoutType (C++11) PODType	TrivialType (C++11) ImplicitLifetimeType
Library-Wide
EqualityComparable LessThanComparable Swappable 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
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)
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)

 

Range adaptor objects are customization point objects that accept viewable_range as their first arguments and return a view. Some range adaptor objects are unary, i.e. they take one viewable_range as their only argument. Other range adaptor objects take a viewable_range and other trailing arguments.

If a range adaptor object takes only one argument, it is also a RangeAdaptorClosureObject.

If a range adaptor object takes more than one argument, it also supports partial application: let

• a be such a range adaptor object, and
• args... be arguments (generally suitable for trailing arguments),

expression a(args...) has following properties:

• it is valid if and only if for every argument e in args... such that E is decltype((e)), std::is_constructible_v<std::decay_t<E>, E> is true,
• when the call is valid, its result object stores a subobject of type std::decay_t<E> direct-non-list-initialized with std::forward<E>(e), for every argument e in args... (in other words, range adaptor objects bind arguments by value),
• the result object is a RangeAdaptorClosureObject,
• calling the RangeAdaptorClosureObject forwards the bound arguments (if any) to the associated range adaptor object. The bound arguments (if any) are considered to have the value category and cv-qualification of the RangeAdaptorClosureObject. In other words, a(args...)(r) is equivalent to std::bind_back(a, args...)(r) (but the former also supports the pipe syntax). (since C++23)

Like other customization point objects, let

• a be an object of the cv-unqualified version of the type of any range adaptor objects,
• args... be any group of arguments that satisfies the constraints of the operator() of the type of a,

calls to

• a(args...),
• std::as_const(a)(args...),
• std::move(a)(args...), and
• std::move(std::as_const(a))(args...)

are all equivalent.

The result object of each of these expressions is either a view object or a RangeAdaptorClosureObject.

Notes

operator() is unsupported for volatile-qualified or const-volatile-qualified version of range adaptor object types. Arrays and functions are converted to pointers while binding.