23 General utilities library [utilities]
The library provides basic function object classes for all of the comparison
operators in the language (
[expr.rel],
[expr.eq])
.For templates
less,
greater,
less_equal, and
greater_equal, the specializations for any pointer type
yield a strict total order that is consistent among those specializations and
is also consistent with the partial order imposed by
the built-in operators
<,
>,
<=,
>=.[
Note: When
a < b is well-defined
for pointers
a and
b of type
P,
this implies
(a < b) == less<P>(a, b),
(a > b) == greater<P>(a, b), and so forth
. —
end note ]
For template specializations
less<void>,
greater<void>,
less_equal<void>, and
greater_equal<void>,
if the call operator calls a built-in operator comparing pointers,
the call operator yields a strict total order
that is consistent among those specializations and
is also consistent with the partial order imposed by those built-in operators
.template <class T = void> struct equal_to {
constexpr bool operator()(const T& x, const T& y) const;
};
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;
};
template <class T, class U> constexpr auto operator()(T&& t, U&& u) const
-> decltype(std::forward<T>(t) == std::forward<U>(u));
Returns: std::forward<T>(t) == std::forward<U>(u). template <class T = void> struct not_equal_to {
constexpr bool operator()(const T& x, const T& y) const;
};
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;
};
template <class T, class U> constexpr auto operator()(T&& t, U&& u) const
-> decltype(std::forward<T>(t) != std::forward<U>(u));
Returns: std::forward<T>(t) != std::forward<U>(u). template <class T = void> struct greater {
constexpr bool operator()(const T& x, const T& y) const;
};
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;
};
template <class T, class U> constexpr auto operator()(T&& t, U&& u) const
-> decltype(std::forward<T>(t) > std::forward<U>(u));
Returns: std::forward<T>(t) > std::forward<U>(u). template <class T = void> struct less {
constexpr bool operator()(const T& x, const T& y) const;
};
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;
};
template <class T, class U> constexpr auto operator()(T&& t, U&& u) const
-> decltype(std::forward<T>(t) < std::forward<U>(u));
Returns: std::forward<T>(t) < std::forward<U>(u). template <class T = void> struct greater_equal {
constexpr bool operator()(const T& x, const T& y) const;
};
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;
};
template <class T, class U> constexpr auto operator()(T&& t, U&& u) const
-> decltype(std::forward<T>(t) >= std::forward<U>(u));
Returns: std::forward<T>(t) >= std::forward<U>(u). template <class T = void> struct less_equal {
constexpr bool operator()(const T& x, const T& y) const;
};
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;
};
template <class T, class U> constexpr auto operator()(T&& t, U&& u) const
-> decltype(std::forward<T>(t) <= std::forward<U>(u));
Returns: std::forward<T>(t) <= std::forward<U>(u).