23 General utilities library [utilities]

23.14 Function objects [function.objects]

23.14.7 Comparisons [comparisons]

23.14.7.4 Class template less [comparisons.less]

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;

Returns: x < y.

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).