std::aligned_union (3) - Linux Manuals
Defined in header <type_traits>
template< std::size_t Len, class... Types > (since C++11)
Provides the nested type type, which is a trivial standard-layout type of a size and alignment suitable for use as uninitialized storage for an object of any of the types listed in Types. The size of the storage is at least Len. std::aligned_union also determines the strictest (largest) alignment requirement among all Types and makes it available as the constant alignment_value.
If sizeof...(Types) == 0 or if any of the types in Types is not a complete object type, the behavior is undefined.
It is implementation-defined whether any extended_alignment is supported.
type the trivial type suitable for storage of any type from Types
template< std::size_t Len, class... Types > (since C++14)
using aligned_union_t = typename aligned_union<Len,Types...>::type;
alignment_value the strictest alignment requirement of all Types
This section is incomplete
Reason: no example
The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
DR Applied to Behavior as published Correct behavior
LWG_2979 C++11 complete type wasn't required requires complete types
alignment_of obtains the type's alignment requirements
aligned_storage defines the type suitable for use as uninitialized storage for types of given size