To enable old function adaptors to manipulate function objects that take one or two arguments, many of the function objects in this International Standard correspondingly provide typedef-names argument_type and result_type for function objects that take one argument and first_argument_type, second_argument_type, and result_type for function objects that take two arguments.
The following member names are defined in addition to names specified in Clause [function.objects]:
namespace std {
template<class T> struct owner_less<shared_ptr<T>> {
using result_type = bool;
using first_argument_type = shared_ptr<T>;
using second_argument_type = shared_ptr<T>;
};
template<class T> struct owner_less<weak_ptr<T>> {
using result_type = bool;
using first_argument_type = weak_ptr<T>;
using second_argument_type = weak_ptr<T>;
};
template <class T> class reference_wrapper {
public :
using result_type = see below; // not always defined
using argument_type = see below; // not always defined
using first_argument_type = see below; // not always defined
using second_argument_type = see below; // not always defined
};
template <class T> struct plus {
using first_argument_type = T;
using second_argument_type = T;
using result_type = T;
};
template <class T> struct minus {
using first_argument_type = T;
using second_argument_type = T;
using result_type = T;
};
template <class T> struct multiplies {
using first_argument_type = T;
using second_argument_type = T;
using result_type = T;
};
template <class T> struct divides {
using first_argument_type = T;
using second_argument_type = T;
using result_type = T;
};
template <class T> struct modulus {
using first_argument_type = T;
using second_argument_type = T;
using result_type = T;
};
template <class T> struct negate {
using argument_type = T;
using result_type = T;
};
template <class T> struct equal_to {
using first_argument_type = T;
using second_argument_type = T;
using result_type = bool;
};
template <class T> struct not_equal_to {
using first_argument_type = T;
using second_argument_type = T;
using result_type = bool;
};
template <class T> struct greater {
using first_argument_type = T;
using second_argument_type = T;
using result_type = bool;
};
template <class T> struct less {
using first_argument_type = T;
using second_argument_type = T;
using result_type = bool;
};
template <class T> struct greater_equal {
using first_argument_type = T;
using second_argument_type = T;
using result_type = bool;
};
template <class T> struct less_equal {
using first_argument_type = T;
using second_argument_type = T;
using result_type = bool;
};
template <class T> struct logical_and {
using first_argument_type = T;
using second_argument_type = T;
using result_type = bool;
};
template <class T> struct logical_or {
using first_argument_type = T;
using second_argument_type = T;
using result_type = bool;
};
template <class T> struct logical_not {
using argument_type = T;
using result_type = bool;
};
template <class T> struct bit_and {
using first_argument_type = T;
using second_argument_type = T;
using result_type = T;
};
template <class T> struct bit_or {
using first_argument_type = T;
using second_argument_type = T;
using result_type = T;
};
template <class T> struct bit_xor {
using first_argument_type = T;
using second_argument_type = T;
using result_type = T;
};
template <class T> struct bit_not {
using argument_type = T;
using result_type = T;
};
template<class R, class T1>
class function<R(T1)> {
public:
using argument_type = T1;
};
template<class R, class T1, class T2>
class function<R(T1, T2)> {
public:
using first_argument_type = T1;
using second_argument_type = T2;
};
}reference_wrapper<T> has a weak result type. If T is a function type, result_type shall be a synonym for the return type of T.
The template specialization reference_wrapper<T> shall define a nested type named argument_type as a synonym for T1 only if the type T is any of the following:
a function type or a pointer to function type taking one argument of type T1
a pointer to member function R T0::f() cv (where cv represents the member function's cv-qualifiers); the type T1 is cv T0*
a class type where the qualified-id T::argument_type is valid and denotes a type ([temp.deduct]); the type T1 is T::argument_type.
The template instantiation reference_wrapper<T> shall define two nested types named first_argument_type and second_argument_type as synonyms for T1 and T2, respectively, only if the type T is any of the following:
a function type or a pointer to function type taking two arguments of types T1 and T2
a pointer to member function R T0::f(T2) cv (where cv represents the member function's cv-qualifiers); the type T1 is cv T0*
a class type where the qualified-ids T::first_argument_type and T::second_argument_type are both valid and both denote types ([temp.deduct]); the type T1 is T::first_argument_type and the type T2 is T::second_argument_type.
All enabled specializations hash<Key> of hash ([unord.hash]) provide two nested types, result_type and argument_type, which shall be synonyms for size_t and Key, respectively.
The forwarding call wrapper g returned by a call to bind(f, bound_args...) ([func.bind.bind]) shall have a weak result type.
The forwarding call wrapper g returned by a call to bind<R>(f, bound_args...) ([func.bind.bind]) shall have a nested type result_type defined as a synonym for R.
The simple call wrapper returned from a call to mem_fn(pm) shall have a nested type result_type that is a synonym for the return type of pm when pm is a pointer to member function.
The simple call wrapper returned from a call to mem_fn(pm) shall define two nested types named argument_type and result_type as synonyms for cv T* and Ret, respectively, when pm is a pointer to member function with cv-qualifier cv and taking no arguments, where Ret is pm's return type.
The simple call wrapper returned from a call to mem_fn(pm) shall define three nested types named first_argument_type, second_argument_type, and result_type as synonyms for cv T*, T1, and Ret, respectively, when pm is a pointer to member function with cv-qualifier cv and taking one argument of type T1, where Ret is pm's return type.
The following member names are defined in addition to names specified in Clause [containers]:
namespace std {
template <class Key, class T, class Compare, class Allocator>
class map<Key, T, Compare, Allocator>::value_compare {
public:
using result_type = bool;
using first_argument_type = value_type;
using second_argument_type = value_type;
};
template <class Key, class T, class Compare, class Allocator>
class multimap<Key, T, Compare, Allocator>::value_compare {
public:
using result_type = bool;
using first_argument_type = value_type;
using second_argument_type = value_type;
};
}