[#BloombergLP-bslstl-Variant_Function-0b]
= xref:BloombergLP.adoc[BloombergLP]::xref:BloombergLP/bslstl.adoc[bslstl]::Variant_Function
:relfileprefix: ../../
:mrdocs:

Component‐private vtable entry invoking a visitor on alternative `t_INDEX`.

== Synopsis

Declared in `<bslstl_variant.h>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
template<
    class t_RET,
    class t_VISITOR,
    class t_VARIANT,
    size_t t_INDEX>
struct Variant_Function;
----

== Static Member Functions

[cols="1,4"]
|===
| Name| Description
| xref:BloombergLP/bslstl/Variant_Function-0b/functionImpl.adoc[`functionImpl`] 
| This component‐private function invokes the specified `visitor` with the active alternative object of the specified `variant` and implicitly converts the return type to (template parameter) `t_RET`. The pre‐C++17 implementation is limited to invocations of the form `visitor(variant)`. The behavior is undefined unless (template parameter) `t_INDEX` is the index of the active alternative.
|===


== Specializations

[cols="1,4"]
|===
| Name| Description
| xref:BloombergLP/bslstl/Variant_Function-05.adoc[`Variant_Function<void, t_VISITOR, t_VARIANT, t_INDEX>`] 
| This partial specialization is used when `t_RET` is `void`. The visitor is invoked and its return value, if any, is ignored. This partial specialization is necessary because a `void`‐returning function cannot contain a `return` statement with a non‐`void` operand.
|===



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