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.
|
(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) |
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