Difference between revisions of "cpp/utility/in place"
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m (rm {{br}} from title - it does not work in this case.) |
m (rm `inline` in `template<...> inline constexpr`; todo: update <utility> too) |
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{{dcl|num=4|since=c++17|1= | {{dcl|num=4|since=c++17|1= | ||
template< class T > | template< class T > | ||
| − | + | constexpr std::in_place_type_t<T> in_place_type {}; | |
}} | }} | ||
{{dcl|num=5|since=c++17|1= | {{dcl|num=5|since=c++17|1= | ||
| Line 23: | Line 23: | ||
{{dcl|num=6|since=c++17|1= | {{dcl|num=6|since=c++17|1= | ||
template< std::size_t I > | template< std::size_t I > | ||
| − | + | constexpr std::in_place_index_t<I> in_place_index {}; | |
}} | }} | ||
{{dcl end}} | {{dcl end}} | ||
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@1,3,5@ The type/type templates {{tt|std::in_place_t}}, {{tt|std::in_place_type_t}} and {{tt|std::in_place_index_t}} can be used in the constructor's parameter list to match the intended tag. | @1,3,5@ The type/type templates {{tt|std::in_place_t}}, {{tt|std::in_place_type_t}} and {{tt|std::in_place_index_t}} can be used in the constructor's parameter list to match the intended tag. | ||
| − | @2,4,6@ The corresponding {{tt|std::in_place}}, {{tt|std::in_place_type}}, and {{tt|std::in_place_index}} instances of {{v|1,3,5}} are disambiguation tags that can be passed to the constructors | + | @2,4,6@ The corresponding {{tt|std::in_place}}, {{tt|std::in_place_type}}, and {{tt|std::in_place_index}} instances of {{v|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. |
===Standard library=== | ===Standard library=== | ||
| − | The following standard library | + | The following standard library types use {{v|1-6}} as disambiguation tags: |
{{dsc begin}} | {{dsc begin}} | ||
| + | {{dsc inc|cpp/utility/dsc any}} | ||
{{dsc inc|cpp/utility/dsc expected}} | {{dsc inc|cpp/utility/dsc expected}} | ||
| + | {{dsc inc|cpp/utility/functional/dsc move_only_function}} | ||
{{dsc inc|cpp/utility/dsc optional}} | {{dsc inc|cpp/utility/dsc optional}} | ||
{{dsc inc|cpp/utility/dsc variant}} | {{dsc inc|cpp/utility/dsc variant}} | ||
| − | |||
{{dsc end}} | {{dsc end}} | ||
Latest revision as of 02:57, 24 September 2024
| 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) |
| template< class T > constexpr std::in_place_type_t<T> in_place_type {}; |
(4) | (since C++17) |
| template< std::size_t I > struct in_place_index_t { explicit in_place_index_t() = default; }; |
(5) | (since C++17) |
| template< std::size_t I > constexpr std::in_place_index_t<I> in_place_index {}; |
(6) | (since C++17) |
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++17) |
objects that hold instances of any CopyConstructible type (class) |
| (C++23) |
a wrapper that contains either an expected or error value (class template) |
| (C++23) |
move-only wrapper of any callable object that supports qualifiers in a given call signature (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) |
[edit] See also
| (C++23) |
indicates that elements of a range are sorted and unique (tag) |
| indicates that elements of a range are sorted (uniqueness is not required) (tag) |
