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

 

C++

Language

Standard library headers

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Utilities library

Strings library

Containers library

Algorithms library

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Numerics library

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Regular expressions library (C++11)

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Thread support library (C++11)

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Technical Specifications

 

Utilities library

Type support (basic types, RTTI, type traits)

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bitset

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Relational operators

rel_ops::operator!=rel_ops::operator>rel_ops::operator<=rel_ops::operator>=

optional, any and variant (C++17)

optional

any

variant

in_placein_place_typein_place_indexin_place_tin_place_type_tin_place_index_t

Pairs and tuples

pair

tuple (C++11)

apply (C++17)

make_from_tuple (C++17)

piecewise_construct_t (C++11)

piecewise_construct (C++11)

integer_sequence (C++14)

Swap, forward and move

swap

exchange (C++14)

forward (C++11)

move (C++11)

move_if_noexcept (C++11)

Elementary string conversions

to_chars (C++17)

from_chars (C++17)

chars_format (C++17)

Type operations

declval (C++11)

as_const (C++17)

 

Defined in header <utility>
struct in_place_t {     explicit in_place_t() = default; }; inline constexpr std::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 std::in_place_type_t<T> in_place_type{};		(since C++17)
template <size_t I> struct in_place_index_t {     explicit in_place_index_t() = default; }; template <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::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 (since C++17)	a wrapper that may or may not hold an object (class template)
variant (since C++17)	a type-safe discriminated union (class template)
any (since C++17)	Objects that hold instances of any CopyConstructible type. (class)