std::in_place, std::in_place_type, std::in_place_index, std::in_place_t, std::in_place_type_t, std::in_place_index_t

< cpp‎ | utility
Defined in header <utility>
struct in_place_t {

    explicit in_place_t() = default;
};

inline constexpr in_place_t in_place{};
 (since C++17)
template< class T >

struct in_place_type_t {
    explicit in_place_type_t() = default;
};
template< class T >

inline constexpr in_place_type_t<T> in_place_type{};
 (since C++17)
template< std::size_t I >

struct in_place_index_t {
    explicit in_place_index_t() = default;
};
template< std::size_t I >

inline constexpr in_place_index_t<I> in_place_index{};
 (since C++17)

std::in_place, std::in_place_type, and std::in_place_index are disambiguation tags that can be passed to the constructors of std::expected, 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

(C++23)
 a wrapper that contains either an expected or error value
(class template)
(C++17)
 a wrapper that may or may not hold an object
(class template)
(C++17)
 a type-safe discriminated union
(class template)
(C++17)
 objects that hold instances of any CopyConstructible type
(class)