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
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Defined in header
<utility>
struct in_place_t { explicit in_place_t() = default; };
(1)
(since C++17)
inline constexpr std::in_place_t in_place {};
(2)
(since C++17)
template< class T >
struct in_place_type_t { explicit in_place_type_t() = default; };
(3)
(since C++17)
struct in_place_type_t { explicit in_place_type_t() = default; };
template< class T >
constexpr std::in_place_type_t<T> in_place_type {};
(4)
(since C++17)
constexpr std::in_place_type_t<T> in_place_type {};
template< std::size_t I >
struct in_place_index_t { explicit in_place_index_t() = default; };
(5)
(since C++17)
struct in_place_index_t { explicit in_place_index_t() = default; };
template< std::size_t I >
constexpr std::in_place_index_t<I> in_place_index {};
(6)
(since C++17)
constexpr std::in_place_index_t<I> in_place_index {};
1,3,5) The 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.2,4,6) The corresponding
std::in_place, std::in_place_type, and std::in_place_index instances of (1,3,5) are disambiguation tags that can be passed to the constructors to indicate that the contained object should be constructed in-place, and (for the latter two) the type of the object to be constructed.[edit] Standard library
The following standard library types use (1-6) as disambiguation tags:
(C++23)
(class template) [edit]