C++ named requirements: BinaryPredicate

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) (since C++20) value value, the expression bin_pred(*iter1, *iter2) or, respectively, bin_pred(*iter, value), must be contextually convertible to bool.

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 (since C++20).

Requirements

• Predicate
• CopyConstructible (unless otherwise specified)

Standard library

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

unique (C++11)	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 a range of elements (function template)
search_n	searches a range for a number of consecutive copies of an element (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)