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

 

C++

Language

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Named requirements

Language support library

Concepts library (C++20)

Diagnostics library

Utilities library

Strings library

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Numerics library

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Technical Specifications

 

C++ named requirements

Basic
DefaultConstructible CopyAssignable CopyConstructible	MoveAssignable (C++11) MoveConstructible (C++11) Destructible
Type properties
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)

 

Specifies that an instance of the type can be assigned from an rvalue argument.

Requirements

The type T satisfies MoveAssignable if

Given

• t, a modifiable lvalue expression of type T
• rv, an rvalue expression of type T

The following expressions must be valid and have their specified effects

Expression	Return type	Return value	Post-conditions
t = rv	T&	t	If t and rv do not refer to the same object , the value of t is equivalent to the value of rv before the assignment. The new value of rv is unspecified

Notes

The type does not have to implement move assignment operator in order to satisfy this type requirement: a copy assignment operator that takes its parameter by value or as a const Type&, will bind to rvalue argument.

If a MoveAssignable class implements a move assignment operator, it may also implement move semantics to take advantage of the fact that the value of rv after assignment is unspecified.

See also

is_move_assignableis_trivially_move_assignableis_nothrow_move_assignable (C++11)(C++11)(C++11)	checks if a type has a move assignment operator (class template)
assignable_from (C++20)	specifies that a type is assignable from another type (concept)