[variant.swap]

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

## 22.6 Variants [[variant]](variant#swap)

### 22.6.3 Class template variant [[variant.variant]](variant.variant#variant.swap)

#### 22.6.3.7 Swap [variant.swap]

[ð](#lib:swap,variant)

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

[1](#1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L6407)

*Mandates*: is_move_constructible_v<Ti> is true for all i[.](#1.sentence-1)

[2](#2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L6411)

*Preconditions*: Each Ti 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#L6415)

*Effects*: 

- [(3.1)](#3.1)

  If valueless_by_exception() && rhs.valueless_by_exception() no effect[.](#3.1.sentence-1)

- [(3.2)](#3.2)

  Otherwise, if index() == rhs.index(), calls swap(*GET*<i>(*this), *GET*<i>(rhs)) where i is index()[.](#3.2.sentence-1)

- [(3.3)](#3.3)

  Otherwise, exchanges values of rhs and *this[.](#3.3.sentence-1)

[4](#4)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L6426)

*Throws*: If index() == rhs.index(),
any exception thrown by swap(*GET*<i>(*this), *GET*<i>(rhs)) with i being index()[.](#4.sentence-1)

Otherwise, any exception thrown by the move constructor
of Ti or Tj with i being index() and j being rhs.index()[.](#4.sentence-2)

[5](#5)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L6435)

*Remarks*: If an exception is thrown during the call to function swap(*GET*<i>(*this), *GET*<i>(rhs)),
the states of the contained values of *this and of rhs are
determined by the exception safety guarantee of swap for lvalues ofTi with i being index()[.](#5.sentence-1)

If an exception is thrown during the exchange of the values of *this and rhs, the states of the values of *this and of rhs are determined by the exception safety guarantee of variant's move constructor[.](#5.sentence-2)

The exception specification is equivalent to the logical and ofis_nothrow_move_constructible_v<Ti> && is_nothrow_swappable_v<Ti> for all i[.](#5.sentence-3)
