[#BloombergLP-bdlb-Variant_ReturnValueHelper]
= xref:BloombergLP.adoc[BloombergLP]::xref:BloombergLP/bdlb.adoc[bdlb]::Variant_ReturnValueHelper
:relfileprefix: ../../
:mrdocs:

Component‐private helper that detects a visitor `ResultType`.

== Synopsis

Declared in `<bdlb_variant.h>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
template<class VISITOR>
struct Variant_ReturnValueHelper
    : xref:bsl/integral_constant-02.adoc[bsl::integral_constant<bool, sizeof (Variant_ReturnValueHelper_Matcher::match<VISITOR>(0)) == sizeof(Variant_ReturnValueHelper_YesType)>]
----

== Description

Do _not_ use. This meta‐function checks whether the template parameter type `VISITOR` has the member `ResultType` defined using "SFINAE" (Substitution Failure Is Not An Error). A `value` of `true` indicates `VISITOR::ResultType` exists, and `false` otherwise.

== Base Classes

[cols="1,4"]
|===
| Name| Description
| `xref:bsl/integral_constant-02.adoc[bsl::integral_constant<bool, sizeof (Variant_ReturnValueHelper_Matcher::match<VISITOR>(0)) == sizeof(Variant_ReturnValueHelper_YesType)>]`
| Metafunction representing a compile‐time constant of the specified (template parameter) `t_TYPE` with the specified (template parameter) `t_VALUE`.
|===

== Type Aliases

[cols="1,4"]
|===
| Name| Description
| xref:bsl/integral_constant-02/type.adoc[`type`] 
| Alias for this `integral_constant` specialization.
| xref:bsl/integral_constant-02/value_type.adoc[`value_type`] 
| Alias for the (template parameter) `t_TYPE`.
|===


== Member Functions

[cols="1,4"]
|===
| Name| Description
| xref:bsl/integral_constant-02/operator_call.adoc[`operator()`] 
| Return a copy of the template argument `t_VALUE`.
| xref:bsl/integral_constant-02/2conversion.adoc[`operator t_TYPE`] 
| Return a copy of the template argument `t_VALUE`.
|===


== Static Data Members

[cols="1,4"]
|===
| Name| Description
| xref:bsl/integral_constant-02/value.adoc[`value`] 
| The compile‐time constant value of this metafunction.
|===



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