[#BloombergLP-bslstl-Variant_IsTag-01]
= xref:BloombergLP.adoc[BloombergLP]::xref:BloombergLP/bslstl.adoc[bslstl]::Variant_IsTag
:relfileprefix: ../../
:mrdocs:

Determine whether `t_TYPE` is a recognized `bsl::variant` tag type.

== Synopsis

Declared in `<bslstl_variant.h>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
template<class t_TYPE>
struct Variant_IsTag
    : xref:bsl/false_type.adoc[bsl::false_type]
----

== Description

This component‐private metafunction derives from `bsl::true_type` if (template parameter) `t_TYPE` is one of the recognized `bsl::variant` tag types, and from `bsl::false_type` otherwise.

This metafunction requires any cv and ref qualifications to be removed from the queried type.

== Base Classes

[cols="1,4"]
|===
| Name| Description
| `xref:bsl/false_type.adoc[bsl::false_type]`
| Metafunction representing the boolean constant `false`.
|===

== Specializations

[cols="1,4"]
|===
| Name| Description
| xref:BloombergLP/bslstl/Variant_IsTag-08.adoc[`Variant_IsTag<std::allocator_arg_t>`] 
| This explicit specialization derives from `bsl::true_type` for the `bsl::allocator_arg_t` tag type.
| xref:BloombergLP/bslstl/Variant_IsTag-0a.adoc[`Variant_IsTag<bsl::in_place_index_t<t_INDEX>>`] 
| This partial specialization derives from `bsl::true_type` for any specialization of the `bsl::in_place_index_t` tag type.
| xref:BloombergLP/bslstl/Variant_IsTag-07.adoc[`Variant_IsTag<bsl::in_place_type_t<t_TYPE>>`] 
| This partial specialization derives from `bsl::true_type` for any specialization of the `bsl::in_place_type_t` tag type.
|===



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