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std::in_place,std::in_place_type,std::in_place_index,std::in_place_t,(3) C++ Standard Libary std::in_place,std::in_place_type,std::in_place_index,std::in_place_t,(3)


std::in_place,std::in_place_type,std::in_place_index,std::in_place_t, - std::in_place,std::in_place_type,std::in_place_index,std::in_place_t,


Defined in header <utility>
struct in_place_t {

explicit in_place_t() = default; (since C++17)

inline constexpr in_place_t in_place{};
template <class T> struct in_place_type_t {

explicit in_place_type_t() = default;
}; (since C++17)
template <class T>

inline constexpr in_place_type_t<T> in_place_type{};
template <std::size_t I> struct in_place_index_t {

explicit in_place_index_t() = default;
}; (since C++17)
template <std::size_t I>

inline constexpr in_place_index_t<I> in_place_index{};

std::in_place, std::in_place_type, and std::in_place_index are disambiguation tags
that can be passed to the constructors of std::optional, std::variant, and std::any
to indicate that the contained object should be constructed in-place, and (for the
latter two) the type of the object to be constructed.

The corresponding type/type templates std::in_place_t, std::in_place_type_t and
std::in_place_index_t can be used in the constructor's parameter list to match the
intended tag.

See also

optional a wrapper that may or may not hold an object
(C++17) (class template)
variant a type-safe discriminated union
(C++17) (class template)
any Objects that hold instances of any CopyConstructible type.
(C++17) (class)