std::is_aggregate - Man Page

typedef integral_constant< _Tp, __v > type
typedef _Tp value_type

constexpr operator value_type () const noexcept
constexpr value_type operator() () const noexcept

static constexpr _Tp value

struct std::is_aggregate< _Tp >"is_aggregate - true if the type is an aggregate.

Since

C++17