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Standard library header <functional>

This header is part of the function objects library and provides the standard hash function.

Namespaces
placeholders (C++11) Provides placeholders for the unbound arguments in a std::bind expression

Classes
Wrappers
(C++11)
 wraps callable object of any copy constructible type with specified function call signature
(class template)
(C++23)
 wraps callable object of any type with specified function call signature
(class template)
(C++11)
 creates a function object out of a pointer to a member
(function template)
(C++11)
 CopyConstructible and CopyAssignable reference wrapper
(class template)
(C++20)(C++20)
 get the reference type wrapped in std::reference_wrapper
(class template)
Helper classes
(C++11)
 the exception thrown when invoking an empty std::function
(class)
(C++11)
 indicates that an object is std::bind expression or can be used as one
(class template)
(C++11)
 indicates that an object is a standard placeholder or can be used as one
(class template)
Arithmetic operations
function object implementing x + y
(class template)
function object implementing x - y
(class template)
function object implementing x * y
(class template)
function object implementing x / y
(class template)
function object implementing x % y
(class template)
function object implementing -x
(class template)
Comparisons
function object implementing x == y
(class template)
function object implementing x != y
(class template)
function object implementing x > y
(class template)
function object implementing x < y
(class template)
function object implementing x >= y
(class template)
function object implementing x <= y
(class template)
Concept-constrained comparisons
(C++20)
 function object implementing x == y
(class)
(C++20)
 function object implementing x != y
(class)
(C++20)
 function object implementing x > y
(class)
(C++20)
 function object implementing x < y
(class)
(C++20)
 function object implementing x >= y
(class)
(C++20)
 function object implementing x <= y
(class)
(C++20)
 function object implementing x <=> y
(class)
Logical operations
function object implementing x && y
(class template)
function object implementing x || y
(class template)
function object implementing !x
(class template)
Bitwise operations
function object implementing x & y
(class template)
function object implementing x | y
(class template)
function object implementing x ^ y
(class template)
(C++14)
 function object implementing ~x
(class template)
Negators
(C++17)
 creates a function object that returns the complement of the result of the function object it holds
(function template)
Identities
(C++20)
 function object that returns its argument unchanged
(class)
Searchers
(C++17)
 standard C++ library search algorithm implementation
(class template)
(C++17)
 Boyer-Moore search algorithm implementation
(class template)
(C++17)
 Boyer-Moore-Horspool search algorithm implementation
(class template)
Hashing
(C++11)
 hash function object
(class template)
(C++11)
 std::hash specializations for fundamental, enumeration, and pointer types
(class template specialization)

Constants
Defined in namespace std::placeholders
(C++11)
 placeholders for the unbound arguments in a std::bind expression
(constant)

Functions
(C++20)(C++23)
 bind a variable number of arguments, in order, to a function object
(function template)
(C++11)
 binds one or more arguments to a function object
(function template)
(C++11)(C++11)
 creates a std::reference_wrapper with a type deduced from its argument
(function template)
(C++17)(C++23)
 invokes any Callable object with given arguments and possibility to specify return type (since C++23)
(function template)

Deprecated in C++11 and removed in C++17

Base
(deprecated in C++11)(removed in C++17)
 adaptor-compatible unary function base class
(class template)
(deprecated in C++11)(removed in C++17)
 adaptor-compatible binary function base class
(class template)
Binders
(deprecated in C++11)(removed in C++17)
 function object holding a binary function and one of its arguments
(class template)
(deprecated in C++11)(removed in C++17)
 binds one argument to a binary function
(function template)
Function adaptors
(deprecated in C++11)(removed in C++17)
 adaptor-compatible wrapper for a pointer to unary function
(class template)
(deprecated in C++11)(removed in C++17)
 adaptor-compatible wrapper for a pointer to binary function
(class template)
(deprecated in C++11)(removed in C++17)
 creates an adaptor-compatible function object wrapper from a pointer to function
(function template)
(deprecated in C++11)(removed in C++17)
 wrapper for a pointer to nullary or unary member function, callable with a pointer to object
(class template)
(deprecated in C++11)(removed in C++17)
 creates a wrapper from a pointer to member function, callable with a pointer to object
(function template)
(deprecated in C++11)(removed in C++17)
 wrapper for a pointer to nullary or unary member function, callable with a reference to object
(class template)
(deprecated in C++11)(removed in C++17)
 creates a wrapper from a pointer to member function, callable with a reference to object
(function template)

Deprecated in C++17 and removed in C++20

Negators
(deprecated in C++17)(removed in C++20)
 wrapper function object returning the complement of the unary predicate it holds
(class template)
(deprecated in C++17)(removed in C++20)
 wrapper function object returning the complement of the binary predicate it holds
(class template)
(deprecated in C++17)(removed in C++20)
 constructs custom std::unary_negate object
(function template)
(deprecated in C++17)(removed in C++20)
 constructs custom std::binary_negate object
(function template)

Synopsis

namespace std {
  // invoke
  template<class F, class... Args>
    constexpr invoke_result_t<F, Args...> invoke(F&& f, Args&&... args)
      noexcept(is_nothrow_invocable_v<F, Args...>);
  template<class R, class F, class... Args>
    constexpr R invoke_r(F&& f, Args&&... args)
      noexcept(is_nothrow_invocable_r_v<R, F, Args...>);
 
  // 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;
 
  template<class T> struct unwrap_reference;
  template<class T> using unwrap_reference_t = typename unwrap_reference<T>::type;
  template<class T> struct unwrap_ref_decay;
  template<class T> using unwrap_ref_decay_t = typename unwrap_ref_decay<T>::type;
 
  // 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
  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>;
 
  // 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
  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>;
 
  // identity
  struct identity;
 
  // function template not_fn
  template<class F> constexpr /* unspecified */ not_fn(F&& f);
 
  // function templates bind_front and bind_back
  template<class F, class... Args> constexpr /* unspecified */ bind_front(F&&, Args&&...);
  template<class F, class... Args> constexpr /* unspecified */ bind_back(F&&, Args&&...);
 
  // bind
  template<class T> struct is_bind_expression;
  template<class T> struct is_placeholder;
 
  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 description */ _1;
    /* see description */ _2;
               .
               .
               .
    /* see description */ _M;
  }
 
  // member function adaptors
  template<class R, class T>
    constexpr /* unspecified */ mem_fn(R T::*) noexcept;
 
  // 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;
 
  template<class...> class move_only_function; // not defined
 
  template<class R, class... ArgTypes>
    class move_only_function<R(ArgTypes...) /*cv ref*/ noexcept(/*noex*/)>;
 
  // searchers
  template<class ForwardIter, class BinaryPredicate = equal_to<>>
    class default_searcher;
 
  template<class RandomAccessIter,
           class Hash = hash<typename iterator_traits<RandomAccessIter>::value_type>,
           class BinaryPredicate = equal_to<>>
    class boyer_moore_searcher;
 
  template<class RandomAccessIter,
           class Hash = hash<typename iterator_traits<RandomAccessIter>::value_type>,
           class BinaryPredicate = equal_to<>>
    class boyer_moore_horspool_searcher;
 
  // hash function primary template
  template<class T>
    struct hash;
 
  // function object binders
  template<class T>
    inline constexpr bool is_bind_expression_v = is_bind_expression<T>::value;
  template<class T>
    inline constexpr int is_placeholder_v = is_placeholder<T>::value;
 
  namespace ranges {
    // concept-constrained comparisons
    struct equal_to;
    struct not_equal_to;
    struct greater;
    struct less;
    struct greater_equal;
    struct less_equal;
  }
}

Class template std::reference_wrapper 

namespace std {
  template<class T> class reference_wrapper {
  public:
    // types
    using type = T;
 
    // construct/copy/destroy
    template<class U>
      constexpr reference_wrapper(U&&) noexcept(see below);
    constexpr reference_wrapper(const reference_wrapper& x) noexcept;
 
    // assignment
    constexpr reference_wrapper& operator=(const reference_wrapper& x) noexcept;
 
    // access
    constexpr operator T& () const noexcept;
    constexpr T& get() const noexcept;
 
    // invocation
    template<class... ArgTypes>
      constexpr invoke_result_t<T&, ArgTypes...> operator()(ArgTypes&&...) const;
  };
  template<class T>
    reference_wrapper(T&) -> reference_wrapper<T>;
}

Class template std::unwrap_reference 

namespace std {
  template<class T>
    struct unwrap_reference;
}

Class template std::unwrap_ref_decay 

namespace std {
  template<class T>
    struct unwrap_ref_decay;
}

Class template std::plus 

namespace std {
  template<class T = void> struct plus {
    constexpr T operator()(const T& x, const T& y) const;
  };
 
  template<> struct plus<void> {
    template<class T, class U> constexpr auto operator()(T&& t, U&& u) const
      -> decltype(std::forward<T>(t) + std::forward<U>(u));
 
    using is_transparent = /* unspecified */;
  };
}

Class template std::minus 

namespace std {
  template<class T = void> struct minus {
    constexpr T operator()(const T& x, const T& y) const;
  };
 
  template<> struct minus<void> {
    template<class T, class U> constexpr auto operator()(T&& t, U&& u) const
      -> decltype(std::forward<T>(t) - std::forward<U>(u));
 
    using is_transparent = /* unspecified */;
  };
}

Class template std::multiplies 

namespace std {
  template<class T = void> struct multiplies {
    constexpr T operator()(const T& x, const T& y) const;
  };
 
  template<> struct multiplies<void> {
    template<class T, class U> constexpr auto operator()(T&& t, U&& u) const
      -> decltype(std::forward<T>(t) * std::forward<U>(u));
 
    using is_transparent = /* unspecified */;
  };
}

Class template std::divides 

namespace std {
  template<class T = void> struct divides {
    constexpr T operator()(const T& x, const T& y) const;
  };
 
  template<> struct divides<void> {
    template<class T, class U> constexpr auto operator()(T&& t, U&& u) const
      -> decltype(std::forward<T>(t) / std::forward<U>(u));
 
    using is_transparent = /* unspecified */;
  };
}

Class template std::modulus 

namespace std {
  template<class T = void> struct modulus {
    constexpr T operator()(const T& x, const T& y) const;
  };
 
  template<> struct modulus<void> {
    template<class T, class U> constexpr auto operator()(T&& t, U&& u) const
      -> decltype(std::forward<T>(t) % std::forward<U>(u));
 
    using is_transparent = /* unspecified */;
  };
}

Class template std::negate 

namespace std {
  template<class T = void> struct negate {
    constexpr T operator()(const T& x) const;
  };
 
  template<> struct negate<void> {
    template<class T> constexpr auto operator()(T&& t) const
      -> decltype(-std::forward<T>(t));
 
    using is_transparent = /* unspecified */;
  };
}

Class template std::equal_to 

namespace std {
  template<class T = void> struct equal_to {
    constexpr bool operator()(const T& x, const T& y) const;
  };
 
  template<> struct equal_to<void> {
    template<class T, class U> constexpr auto operator()(T&& t, U&& u) const
      -> decltype(std::forward<T>(t) == std::forward<U>(u));
 
    using is_transparent = /* unspecified */;
  };
}

Class template std::not_equal_to 

namespace std {
  template<class T = void> struct not_equal_to {
    constexpr bool operator()(const T& x, const T& y) const;
  };
 
  template<> struct not_equal_to<void> {
    template<class T, class U> constexpr auto operator()(T&& t, U&& u) const
      -> decltype(std::forward<T>(t) != std::forward<U>(u));
 
    using is_transparent = /* unspecified */;
  };
}

Class template std::greater 

namespace std {
  template<class T = void> struct greater {
    constexpr bool operator()(const T& x, const T& y) const;
  };
 
  template<> struct greater<void> {
    template<class T, class U> constexpr auto operator()(T&& t, U&& u) const
      -> decltype(std::forward<T>(t) > std::forward<U>(u));
 
    using is_transparent = /* unspecified */;
  };
}

Class template std::less 

namespace std {
  template<class T = void> struct less {
    constexpr bool operator()(const T& x, const T& y) const;
  };
 
  template<> struct less<void> {
    template<class T, class U> constexpr auto operator()(T&& t, U&& u) const
      -> decltype(std::forward<T>(t) < std::forward<U>(u));
 
    using is_transparent = /* unspecified */;
  };
}

Class template std::greater_equal 

namespace std {
  template<class T = void> struct greater_equal {
    constexpr bool operator()(const T& x, const T& y) const;
  };
 
  template<> struct greater_equal<void> {
    template<class T, class U> constexpr auto operator()(T&& t, U&& u) const
      -> decltype(std::forward<T>(t) >= std::forward<U>(u));
 
    using is_transparent = /* unspecified */;
  };
}

Class template std::less_equal 

namespace std {
  template<class T = void> struct less_equal {
    constexpr bool operator()(const T& x, const T& y) const;
  };
 
  template<> struct less_equal<void> {
    template<class T, class U> constexpr auto operator()(T&& t, U&& u) const
      -> decltype(std::forward<T>(t) <= std::forward<U>(u));
 
    using is_transparent = /* unspecified */;
  };
}

Class std::ranges::equal_to 

namespace std::ranges {
  struct equal_to {
    template<class T, class U>
    constexpr bool operator()(T&& t, U&& u) const;
 
    using is_transparent = /* unspecified */;
  };
}

Class std::ranges::not_equal_to 

namespace std::ranges {
  struct not_equal_to {
    template<class T, class U>
    constexpr bool operator()(T&& t, U&& u) const;
 
    using is_transparent = /* unspecified */;
  };
}

Class std::ranges::greater 

namespace std::ranges {
  struct greater {
    template<class T, class U>
    constexpr bool operator()(T&& t, U&& u) const;
 
    using is_transparent = /* unspecified */;
  };
}

Class std::ranges::less 

namespace std::ranges {
  struct less {
    template<class T, class U>
    constexpr bool operator()(T&& t, U&& u) const;
 
    using is_transparent = /* unspecified */;
  };
}

Class std::ranges::greater_equal 

namespace std::ranges {
  struct greater_equal {
    template<class T, class U>
    constexpr bool operator()(T&& t, U&& u) const;
 
    using is_transparent = /* unspecified */;
  };
}

Class std::ranges::less_equal 

namespace std::ranges {
  struct less_equal {
    template<class T, class U>
    constexpr bool operator()(T&& t, U&& u) const;
 
    using is_transparent = /* unspecified */;
  };
}

Class template std::logical_and 

namespace std {
  template<class T = void> struct logical_and {
    constexpr bool operator()(const T& x, const T& y) const;
  };
 
  template<> struct logical_and<void> {
    template<class T, class U> constexpr auto operator()(T&& t, U&& u) const
      -> decltype(std::forward<T>(t) && std::forward<U>(u));
 
    using is_transparent = /* unspecified */;
  };
}

Class template std::logical_or 

namespace std {
  template<class T = void> struct logical_or {
    constexpr bool operator()(const T& x, const T& y) const;
  };
 
  template<> struct logical_or<void> {
    template<class T, class U> constexpr auto operator()(T&& t, U&& u) const
      -> decltype(std::forward<T>(t) || std::forward<U>(u));
 
    using is_transparent = /* unspecified */;
  };
}

Class template std::logical_not 

namespace std {
  template<class T = void> struct logical_not {
    constexpr bool operator()(const T& x) const;
  };
 
  template<> struct logical_not<void> {
    template<class T> constexpr auto operator()(T&& t) const
      -> decltype(!std::forward<T>(t));
 
    using is_transparent = /* unspecified */;
  };
}

Class template std::bit_and 

namespace std {
  template<class T = void> struct bit_and {
    constexpr T operator()(const T& x, const T& y) const;
  };
 
  template<> struct bit_and<void> {
    template<class T, class U> constexpr auto operator()(T&& t, U&& u) const
      -> decltype(std::forward<T>(t) & std::forward<U>(u));
 
    using is_transparent = /* unspecified */;
  };
}

Class template std::bit_or 

namespace std {
  template<class T = void> struct bit_or {
    constexpr T operator()(const T& x, const T& y) const;
  };
 
  template<> struct bit_or<void> {
    template<class T, class U> constexpr auto operator()(T&& t, U&& u) const
      -> decltype(std::forward<T>(t) | std::forward<U>(u));
 
    using is_transparent = /* unspecified */;
  };
}

Class template std::bit_xor 

namespace std {
  template<class T = void> struct bit_xor {
    constexpr T operator()(const T& x, const T& y) const;
  };
 
  template<> struct bit_xor<void> {
    template<class T, class U> constexpr auto operator()(T&& t, U&& u) const
      -> decltype(std::forward<T>(t) ^ std::forward<U>(u));
 
    using is_transparent = /* unspecified */;
  };
}

Class template std::bit_not 

namespace std {
  template<class T = void> struct bit_not {
    constexpr T operator()(const T& x) const;
  };
 
  template<> struct bit_not<void> {
    template<class T> constexpr auto operator()(T&& t) const
      -> decltype(~std::forward<T>(t));
 
    using is_transparent = /* unspecified */;
  };
}

Class template std::identity 

namespace std {
  struct identity {
    template<class T>
      constexpr T&& operator()(T&& t) const noexcept;
 
    using is_transparent = /* unspecified */;
  };
}

Class template std::is_bind_expression 

namespace std {
  template<class T> struct is_bind_expression;
}

Class template std::is_placeholder 

namespace std {
  template<class T> struct is_placeholder;
}

Class std::bad_function_call 

namespace std {
  class bad_function_call : public exception {
  public:
    // see [exception] for the specification of the special member functions
    const char* what() const noexcept override;
  };
}

Class template std::function 

namespace std {
  template<class> class function; // not defined
 
  template<class R, class... ArgTypes>
  class function<R(ArgTypes...)> {
  public:
    using result_type = R;
 
    // construct/copy/destroy
    function() noexcept;
    function(nullptr_t) noexcept;
    function(const function&);
    function(function&&) noexcept;
    template<class F> function(F);
 
    function& operator=(const function&);
    function& operator=(function&&);
    function& operator=(nullptr_t) noexcept;
    template<class F> function& operator=(F&&);
    template<class F> function& operator=(reference_wrapper<F>) noexcept;
 
    ~function();
 
    // function modifiers
    void swap(function&) noexcept;
 
    // function capacity
    explicit operator bool() const noexcept;
 
    // function invocation
    R operator()(ArgTypes...) const;
 
    // function target access
    const type_info& target_type() const noexcept;
    template<class T>       T* target() noexcept;
    template<class T> const T* target() const noexcept;
  };
 
  template<class R, class... ArgTypes>
    function(R(*)(ArgTypes...)) -> function<R(ArgTypes...)>;
 
  template<class F> function(F) -> function</* see description */>;
 
  // null pointer comparison functions
  template<class R, class... ArgTypes>
    bool operator==(const function<R(ArgTypes...)>&, nullptr_t) noexcept;
 
  // specialized algorithms
  template<class R, class... ArgTypes>
    void swap(function<R(ArgTypes...)>&, function<R(ArgTypes...)>&) noexcept;
}

Class template std::move_only_function 

namespace std {
  template<class... S> class move_only_function; // not defined
 
  template<class R, class... ArgTypes>
  class move_only_function<R(ArgTypes...) /*cv-ref*/ noexcept(/*noex*/)> {
  public:
    using result_type = R;
 
    // construct/move/destroy
    move_only_function() noexcept;
    move_only_function(nullptr_t) noexcept;
    move_only_function(move_only_function&&) noexcept;
    template<class F> move_only_function(F&&);
 
    template<class T, class... Args>
      explicit move_only_function(in_place_type_t<T>, Args&&...);
    template<class T, class U, class... Args>
      explicit move_only_function(in_place_type_t<T>, initializer_list<U>, Args&&...);
 
    move_only_function& operator=(move_only_function&&);
    move_only_function& operator=(nullptr_t) noexcept;
    template<class F> move_only_function& operator=(F&&);
 
    ~move_only_function();
 
    // move_only_function invocation
    explicit operator bool() const noexcept;
 
    R operator()(ArgTypes...) /*cv-ref*/ noexcept(/*noex*/);
 
    // move_only_function utility
    void swap(move_only_function&) noexcept;
 
    friend void swap(move_only_function&, move_only_function&) noexcept;
 
    friend bool operator==(const move_only_function&, nullptr_t) noexcept;
 
  private:
    template<class VT>
      static constexpr bool /*is-callable-from*/ = /* see description */; // exposition-only
  };
}

Class template std::default_searcher 

namespace std {
  template<class ForwardIter1, class BinaryPredicate = equal_to<>>
    class default_searcher {
    public:
      constexpr default_searcher(ForwardIter1 pat_first, ForwardIter1 pat_last,
                                 BinaryPredicate pred = BinaryPredicate());
 
      template<class ForwardIter2>
        constexpr pair<ForwardIter2, ForwardIter2>
          operator()(ForwardIter2 first, ForwardIter2 last) const;
 
    private:
      ForwardIter1 pat_first_;            // exposition only
      ForwardIter1 pat_last_;             // exposition only
      BinaryPredicate pred_;              // exposition only
  };
}

Class template std::boyer_moore_searcher 

namespace std {
  template<class RandomAccessIter1,
           class Hash = hash<typename iterator_traits<RandomAccessIter1>::value_type>,
           class BinaryPredicate = equal_to<>>
    class boyer_moore_searcher {
    public:
      boyer_moore_searcher(RandomAccessIter1 pat_first,
                           RandomAccessIter1 pat_last,
                           Hash hf = Hash(),
                           BinaryPredicate pred = BinaryPredicate());
 
      template<class RandomAccessIter2>
        pair<RandomAccessIter2, RandomAccessIter2>
          operator()(RandomAccessIter2 first, RandomAccessIter2 last) const;
 
    private:
      RandomAccessIter1 pat_first_;       // exposition only
      RandomAccessIter1 pat_last_;        // exposition only
      Hash hash_;                         // exposition only
      BinaryPredicate pred_;              // exposition only
    };
}

Class template std::boyer_moore_horspool_searcher 

namespace std {
  template<class RandomAccessIter1,
           class Hash = hash<typename iterator_traits<RandomAccessIter1>::value_type>,
           class BinaryPredicate = equal_to<>>
    class boyer_moore_horspool_searcher {
    public:
      boyer_moore_horspool_searcher(RandomAccessIter1 pat_first,
                                    RandomAccessIter1 pat_last,
                                    Hash hf = Hash(),
                                    BinaryPredicate pred = BinaryPredicate());
 
      template<class RandomAccessIter2>
        pair<RandomAccessIter2, RandomAccessIter2>
          operator()(RandomAccessIter2 first, RandomAccessIter2 last) const;
 
    private:
      RandomAccessIter1 pat_first_;       // exposition only
      RandomAccessIter1 pat_last_;        // exposition only
      Hash hash_;                         // exposition only
      BinaryPredicate pred_;              // exposition only
  };
}

See also

<string> Specializes std::hash for std::string, std::u16string, std::u32string, std::wstring
<string_view> Specializes std::hash for std::string_view, std::u16string_view, std::u32string_view, std::wstring_view
<system_error> Specializes std::hash for std::error_code
<bitset> Specializes std::hash for std::bitset
<memory> Specializes std::hash for std::unique_ptr, std::shared_ptr
<typeindex> Specializes std::hash for std::type_index
<vector> Specializes std::hash for std::vector<bool>
<thread> Specializes std::hash for std::thread::id
<optional> Specializes std::hash for std::optional
<variant> Specializes std::hash for std::variant
<coroutine> Specializes std::hash for std::coroutine_handle
<stacktrace> Specializes std::hash for std::stacktrace_entry and std::basic_stacktrace

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