[#BloombergLP-bslma-AllocatorUtil-swap-075bea]
= xref:BloombergLP.adoc[BloombergLP]::xref:BloombergLP/bslma.adoc[bslma]::xref:BloombergLP/bslma/AllocatorUtil.adoc[AllocatorUtil]::swap
:relfileprefix: ../../../
:mrdocs:

Conditionally swap the values at `pa` and `pb` based on `allowed`.

== Synopsis

Declared in `<bslma_allocatorutil.h>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
template<class t_TYPE>
static
void
swap(
    t_TYPE* pa,
    t_TYPE* pb,
    xref:bsl/false_type.adoc[bsl::false_type] allowed);
----

== Description

If the specified `allowed` tag is `bsl::true_type`, swap the values of allocators at the specified `pa` and `pb` addresses using ADL swap (with `std::swap` in scope); otherwise, do nothing. The `t_TYPE` template parameter is typically an allocator type and the `allowed` flag is typically a propagation trait dependant on the calling context, such as `propagate_on_container_swap`. Instantiation will fail if `allowed` is `false_type` and `t_TYPE` is not swappable (i.e., because it lacks a publically available assignment operator). The behavior is undefined unless `allowed` is `true_type` or '*pa == *pb' before the call.

== Parameters

[cols="1,4"]
|===
| Name| Description
| *pa*
| address of the first object to swap
| *pb*
| address of the second object to swap
| *allowed*
| whether swapping is permitted
|===


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