C++ named requirements: LessThanComparable

 

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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
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Container SequenceContainer ContiguousContainer (C++17)	ReversibleContainer AssociativeContainer AllocatorAwareContainer	UnorderedAssociativeContainer (C++11)
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DefaultInsertable (C++11) CopyInsertable (C++11)	MoveInsertable (C++11) EmplaceConstructible (C++11)	Erasable (C++11)
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LegacyIterator LegacyOutputIterator LegacyInputIterator	LegacyForwardIterator LegacyBidirectionalIterator LegacyRandomAccessIterator	LegacyContiguousIterator (C++17) ConstexprIterator (C++20)
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FormattedInputFunction UnformattedInputFunction	FormattedOutputFunction	UnformattedOutputFunction
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BasicFormatter (C++20)	Formatter (C++20)
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SeedSequence (C++11) RandomNumberEngine (C++11)	RandomNumberDistribution (C++11) UniformRandomBitGenerator (C++11)	RandomNumberEngineAdaptor (C++11)
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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)
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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)

 

The type must work with < operator and the result should have standard semantics.

Requirements

The type T satisfies LessThanComparable if

Given

• a, b, and c, expressions of type T or const T

The following expressions must be valid and have their specified effects

Expression	Return type	Requirements
a < b	implicitly convertible to bool	Establishes strict weak ordering relation with the following properties For all a, !(a < a) If a < b then !(b < a) If a < b and b < c then a < c Defining equiv(a, b) as !(a < b) && !(b < a), if equiv(a, b) and equiv(b, c), then equiv(a, c)

Notes

To satisfy this requirement, types that do not have built-in comparison operators have to provide a user-defined operator<.

For the types that are both EqualityComparable and LessThanComparable, the C++ standard library makes a distinction between equality, which is the value of the expression a == b and equivalence, which is the value of the expression !(a < b) && !(b < a).

See also

Compare

a BinaryPredicate that establishes an ordering relation (named requirement)