20 General utilities library [utilities]

20.14 Function objects [function.objects]

20.14.2 Header <functional> synopsis [functional.syn]

namespace std { // [func.invoke], invoke template<class F, class... Args> constexpr invoke_result_t<F, Args...> invoke(F&& f, Args&&... args) noexcept(is_nothrow_invocable_v<F, Args...>); // [refwrap], reference_­wrapper template<class T> class reference_wrapper; template<class T> constexpr reference_wrapper<T> ref(T&) noexcept; template<class T> constexpr reference_wrapper<const T> cref(const T&) noexcept; template<class T> void ref(const T&&) = delete; template<class T> void cref(const T&&) = delete; template<class T> constexpr reference_wrapper<T> ref(reference_wrapper<T>) noexcept; template<class T> constexpr reference_wrapper<const T> cref(reference_wrapper<T>) noexcept; // [arithmetic.operations], arithmetic operations template<class T = void> struct plus; template<class T = void> struct minus; template<class T = void> struct multiplies; template<class T = void> struct divides; template<class T = void> struct modulus; template<class T = void> struct negate; template<> struct plus<void>; template<> struct minus<void>; template<> struct multiplies<void>; template<> struct divides<void>; template<> struct modulus<void>; template<> struct negate<void>; // [comparisons], comparisons template<class T = void> struct equal_to; template<class T = void> struct not_equal_to; template<class T = void> struct greater; template<class T = void> struct less; template<class T = void> struct greater_equal; template<class T = void> struct less_equal; template<> struct equal_to<void>; template<> struct not_equal_to<void>; template<> struct greater<void>; template<> struct less<void>; template<> struct greater_equal<void>; template<> struct less_equal<void>; // [comparisons.three.way], class compare_­three_­way struct compare_three_way; // [logical.operations], logical operations template<class T = void> struct logical_and; template<class T = void> struct logical_or; template<class T = void> struct logical_not; template<> struct logical_and<void>; template<> struct logical_or<void>; template<> struct logical_not<void>; // [bitwise.operations], bitwise operations template<class T = void> struct bit_and; template<class T = void> struct bit_or; template<class T = void> struct bit_xor; template<class T = void> struct bit_not; template<> struct bit_and<void>; template<> struct bit_or<void>; template<> struct bit_xor<void>; template<> struct bit_not<void>; // [func.identity], identity struct identity; // [func.not.fn], function template not_­fn template<class F> constexpr unspecified not_fn(F&& f); // [func.bind.front], function template bind_­front template<class F, class... Args> constexpr unspecified bind_front(F&&, Args&&...); // [func.bind], bind template<class T> struct is_bind_expression; template<class T> inline constexpr bool is_bind_expression_v = is_bind_expression<T>::value; template<class T> struct is_placeholder; template<class T> inline constexpr int is_placeholder_v = is_placeholder<T>::value; template<class F, class... BoundArgs> constexpr unspecified bind(F&&, BoundArgs&&...); template<class R, class F, class... BoundArgs> constexpr unspecified bind(F&&, BoundArgs&&...); namespace placeholders { // M is the implementation-defined number of placeholders see below _1; see below _2; . . . see below _M; } // [func.memfn], member function adaptors template<class R, class T> constexpr unspecified mem_fn(R T::*) noexcept; // [func.wrap], polymorphic function wrappers class bad_function_call; template<class> class function; // not defined template<class R, class... ArgTypes> class function<R(ArgTypes...)>; template<class R, class... ArgTypes> void swap(function<R(ArgTypes...)>&, function<R(ArgTypes...)>&) noexcept; template<class R, class... ArgTypes> bool operator==(const function<R(ArgTypes...)>&, nullptr_t) noexcept; // [func.search], searchers template<class ForwardIterator, class BinaryPredicate = equal_to<>> class default_searcher; template<class RandomAccessIterator, class Hash = hash<typename iterator_traits<RandomAccessIterator>::value_type>, class BinaryPredicate = equal_to<>> class boyer_moore_searcher; template<class RandomAccessIterator, class Hash = hash<typename iterator_traits<RandomAccessIterator>::value_type>, class BinaryPredicate = equal_to<>> class boyer_moore_horspool_searcher; // [unord.hash], class template hash template<class T> struct hash; namespace ranges { // [range.cmp], concept-constrained comparisons struct equal_to; struct not_equal_to; struct greater; struct less; struct greater_equal; struct less_equal; } }
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[Example 1:
If a C++ program wants to have a by-element addition of two vectors a and b containing double and put the result into a, it can do: transform(a.begin(), a.end(), b.begin(), a.begin(), plus<double>());
— end example]
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[Example 2:
To negate every element of a: transform(a.begin(), a.end(), a.begin(), negate<double>());
— end example]