[#BloombergLP-bdlb-VariantImp-apply-075f]
= xref:BloombergLP.adoc[BloombergLP]::xref:BloombergLP/bdlb.adoc[bdlb]::xref:BloombergLP/bdlb/VariantImp.adoc[VariantImp]::apply
:relfileprefix: ../../../
:mrdocs:

Apply `visitor` to the held `TYPE` value of this variant.

== Synopsis

Declared in `<bdlb_variant.h>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
template<
    class VISITOR,
    class TYPE>
VISITOR::ResultType
apply(
    VISITOR const& visitor,
    TYPE const& defaultValue) const
requires Variant_ReturnValueHelper<VISITOR>::value == 1;
----

== Description

If this variant is unset, the specified `defaultValue` of template parameter `TYPE` is passed to the `visitor`. `TYPE` must be the same as one of the types that this variant can hold. The behavior is undefined unless this variant is unset or holds a value of template parameter `TYPE`. Note that this method is selected only if the template parameter type `VISITOR` defines a `typedef` of `ResultType` in its public interface. Also note that this method is defined inline to work around a Windows compiler bug with SFINAE functions.

== Return Value

result of invoking `visitor` on the active alternative

== Parameters

[cols="1,4"]
|===
| Name| Description
| *visitor*
| callable applied to the active alternative
| *defaultValue*
| value passed to `visitor` when this variant is unset
|===


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