C++ named requirements: BinaryPredicate - cppreference.com (original) (raw)
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.
[edit] Requirements
- Predicate
- CopyConstructible (unless otherwise specified)
[edit] 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>) [edit] |
|---|---|
| unique | removes consecutive duplicate elements (public member function of std::list<T,Allocator>) [edit] |
| find_end | finds the last sequence of elements in a certain range (function template) [edit] |
| find_first_of | searches for any one of a set of elements (function template) [edit] |
| adjacent_find | finds the first two adjacent items that are equal (or satisfy a given predicate) (function template) [edit] |
| mismatch | finds the first position where two ranges differ (function template) [edit] |
| equal | determines if two sets of elements are the same (function template) [edit] |
| is_permutation(C++11) | determines if a sequence is a permutation of another sequence (function template) [edit] |
| search | searches for the first occurrence of a range of elements (function template) [edit] |
| search_n | searches for the first occurrence of a number consecutive copies of an element in a range (function template) [edit] |
| unique | removes consecutive duplicate elements in a range (function template) [edit] |
| unique_copy | creates a copy of some range of elements that contains no consecutive duplicates (function template) [edit] |
| not2(deprecated in C++17)(removed in C++20) | constructs custom std::binary_negate object (function template) [edit] |
| unordered_set(C++11) | collection of unique keys, hashed by keys (class template) [edit] |
| unordered_map(C++11) | collection of key-value pairs, hashed by keys, keys are unique (class template) [edit] |
| unordered_multiset(C++11) | collection of keys, hashed by keys (class template) [edit] |
| unordered_multimap(C++11) | collection of key-value pairs, hashed by keys (class template) [edit] |
[edit] 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 weakto reflect the expectation of implementations | requirements strengthened |
| LWG 3031 | C++98 | requirements on const values were insufficent | requirements strengthened |