C++ named requirements: BinaryPredicate

 

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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)

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BinaryPredicate is a set of requirements expected by some of the standard library facilities from the user-provided arguments.

Given a BinaryPredicate bin_pred and a pair of iterators iter1 and iter2 or an iterator iter and a (possibly const) value value, the type and value category of the expression bin_pred(*iter1, *iter2) or, respectively, bin_pred(*iter, value), must meet the BooleanTestable requirements.

In addition, evaluation of that expression is not allowed to call non-const member functions of the dereferenced iterators; syntactically, the predicate must accept const object arguments, with the same behavior regardless of whether its arguments are const or non-const.

Requirements

• Predicate
• CopyConstructible (unless otherwise specified)

Standard library

The following standard library facilities expect a BinaryPredicate which isn't a Compare type.

unique	removes consecutive duplicate elements (public member function of std::forward_list<T,Allocator>)
unique	removes consecutive duplicate elements (public member function of std::list<T,Allocator>)
find_end	finds the last sequence of elements in a certain range (function template)
find_first_of	searches for any one of a set of elements (function template)
adjacent_find	finds the first two adjacent items that are equal (or satisfy a given predicate) (function template)
mismatch	finds the first position where two ranges differ (function template)
equal	determines if two sets of elements are the same (function template)
is_permutation (C++11)	determines if a sequence is a permutation of another sequence (function template)
search	searches for the first occurrence of a range of elements (function template)
search_n	searches for the first occurrence of a number consecutive copies of an element in a range (function template)
unique	removes consecutive duplicate elements in a range (function template)
unique_copy	creates a copy of some range of elements that contains no consecutive duplicates (function template)
not2 (deprecated in C++17)(removed in C++20)	constructs custom std::binary_negate object (function template)
unordered_set (C++11)	collection of unique keys, hashed by keys (class template)
unordered_map (C++11)	collection of key-value pairs, hashed by keys, keys are unique (class template)
unordered_multiset (C++11)	collection of keys, hashed by keys (class template)
unordered_multimap (C++11)	collection of key-value pairs, hashed by keys (class template)

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR	Applied to	Behavior as published	Correct behavior
LWG 2114 (P2167R3)	C++98	convertibility of return types to bool was too weak to reflect the expectation of implementations	requirements strengthened
LWG 3031	C++98	requirements on const values were insufficent	requirements strengthened