[#bsl-swap-0f5]
= xref:bsl.adoc[bsl]::swap
:relfileprefix: ../
:mrdocs:

Efficiently exchange the values of the specified `lhs` and `rhs` objects. This method provides the no‐throw guarantee if the two variant objects being swapped have the same active alternative and that alternative provides that guarantee; otherwise, this method provides the basic guarantee. If `lhs` and `rhs` do not contain the same alternative or they have unequal allocators, and an exception is thrown during the swap, either or both variant objects may be left in a valueless state or with an alternative in a moved‐from state. All alternatives shall be move constructible and swappable. For simplicity of implementation, this function differs from the standard in the following : * constraints are not implemented * constexpr is not implemented

== Synopsis

Declared in `<bslstl_variant.h>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
template<
    class t_HEAD,
    class... t_TAIL>
void
swap(
    xref:bsl/variant.adoc[bsl::variant<t_HEAD, t_TAIL...>]& lhs,
    xref:bsl/variant.adoc[bsl::variant<t_HEAD, t_TAIL...>]& rhs);
----


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