[#bsl-swap-05b]
= xref:bsl.adoc[bsl]::swap
:relfileprefix: ../
:mrdocs:

Exchange the value, hasher, key‐equality functor, and `max_load_factor` of the specified `a` object with those of the specified `b` object; also exchange the allocator of `a` with that of `b` if the (template parameter) type `ALLOCATOR` has the `propagate_on_container_swap` trait, and do not modify either allocator otherwise. This function provides the no‐throw exception‐safety guarantee if and only if both the (template parameter) types `HASH` and `EQUAL` provide no‐throw swap operations; if an exception is thrown, both objects are left in valid but unspecified states. This operation guarantees `O[1]` complexity. The behavior is undefined unless either `a` was created with the same allocator as `b` or `ALLOCATOR` has the `propagate_on_container_swap` trait.

== Synopsis

Declared in `<bslstl_unorderedset.h>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
template<
    class KEY,
    class HASH,
    class EQUAL,
    class ALLOCATOR>
void
swap(
    xref:bsl/unordered_set-0d2d.adoc[unordered_set<KEY, HASH, EQUAL, ALLOCATOR>]& a,
    xref:bsl/unordered_set-0d2d.adoc[unordered_set<KEY, HASH, EQUAL, ALLOCATOR>]& b) noexcept(noexcept(a.swap(b)));
----


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