[optional.swap]

# 22 General utilities library [[utilities]](./#utilities)

## 22.5 Optional objects [[optional]](optional#swap)

### 22.5.3 Class template optional [[optional.optional]](optional.optional#optional.swap)

#### 22.5.3.5 Swap [optional.swap]

[🔗](#lib:swap,optional)

`constexpr void swap(optional& rhs) noexcept(see below);
`

[1](#1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L3999)

*Mandates*: is_move_constructible_v<T> is true[.](#1.sentence-1)

[2](#2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L4003)

*Preconditions*: T meets the [*Cpp17Swappable*](swappable.requirements#:Cpp17Swappable "16.4.4.3 Swappable requirements [swappable.requirements]") requirements ([[swappable.requirements]](swappable.requirements "16.4.4.3 Swappable requirements"))[.](#2.sentence-1)

[3](#3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L4007)

*Effects*: See Table [71](#tab:optional.swap "Table 71: optional​::​swap(optional&amp;) effects")[.](#3.sentence-1)

Table [71](#tab:optional.swap) — optional​::​swap(optional&) effects [[tab:optional.swap]](./tab:optional.swap)  

| [🔗](#tab:optional.swap-row-1) |  | ***this contains a value** | ***this does not contain a value** |
| --- | --- | --- | --- |
| [🔗](#tab:optional.swap-row-2)<br>**rhs contains a value** |  | calls swap(*(*this), *rhs) | direct-non-list-initializes the contained value of *this with std​::​move(*rhs), followed by rhs.val->T​::​~T(); postcondition is that *this contains a value and rhs does not contain a value |
| [🔗](#tab:optional.swap-row-3)<br>**rhs does not contain a value** |  | direct-non-list-initializes the contained value of rhs with std​::​move(*(*this)), followed by val->T​::​~T(); postcondition is that *this does not contain a value and rhs contains a value | no effect |

[4](#4)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L4030)

*Throws*: Any exceptions thrown by the operations in the relevant part of Table [71](#tab:optional.swap "Table 71: optional​::​swap(optional&amp;) effects")[.](#4.sentence-1)

[5](#5)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L4034)

*Remarks*: The exception specification is equivalent to:is_nothrow_move_constructible_v<T> && is_nothrow_swappable_v<T>

[6](#6)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L4041)

If any exception is thrown, the results of the expressions this->has_value() and rhs.has_value() remain unchanged[.](#6.sentence-1)

If an exception is thrown during the call to function swap,
the state of *val and *rhs.val is determined by the exception safety guarantee of swap for lvalues of T[.](#6.sentence-2)

If an exception is thrown during the call to T's move constructor,
the state of *val and *rhs.val is determined by the exception safety guarantee of T's move constructor[.](#6.sentence-3)