std::is_aggregate
Defined in header <type_traits>
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template< class T > struct is_aggregate; |
(since C++17) | |
Checks if T
is an aggregate type. The member constant value
is equal to true if T
is an aggregate type and false otherwise.
The behavior is undefined if std::remove_all_extents_t<T> is an incomplete type other than (possibly cv-qualified) void.
Template parameters
T | - | a type to check |
Helper variable template
template< class T > inline constexpr bool is_aggregate_v = is_aggregate<T>::value; |
(since C++17) | |
Inherited from std::integral_constant
Member constants
value [static] |
true if T is an aggregate type , false otherwise (public static member constant) |
Member functions
operator bool |
converts the object to bool, returns value (public member function) |
operator() (C++14) |
returns value (public member function) |
Member types
Type | Definition |
value_type
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bool
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type
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std::integral_constant<bool, value> |
Example
Run this code
#include <type_traits> #include <new> #include <utility> // constructs a T at the uninitialized memory pointed to by p // using list-initialization for aggregates and non-list initialization otherwise template<class T, class... Args> T* construct(T* p, Args&&... args) { if constexpr(std::is_aggregate_v<T>) { return ::new (static_cast<void*>(p)) T{std::forward<Args>(args)...}; } else { return ::new (static_cast<void*>(p)) T(std::forward<Args>(args)...); } } struct A { int x, y; }; struct B { B(int, const char*) { } }; int main() { std::aligned_union_t<1, A, B> storage; A* a = construct(reinterpret_cast<A*>(&storage), 1, 2); B* b = construct(reinterpret_cast<B*>(&storage), 1, "hello"); }