[#BloombergLP-bslstl-Variant_IsTag-01]
= xref:BloombergLP.adoc[BloombergLP]::xref:BloombergLP/bslstl.adoc[bslstl]::Variant&lowbar;IsTag
:relfileprefix: ../../
:mrdocs:

Determine whether `t&lowbar;TYPE` is a recognized `bsl&colon;&colon;variant` tag type&period;

== Synopsis

Declared in `&lt;bslstl&lowbar;variant&period;h&gt;`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
template&lt;class t&lowbar;TYPE&gt;
struct Variant&lowbar;IsTag
    : xref:bsl/false_type.adoc[bsl::false&lowbar;type]
----

== Description

This component&hyphen;private metafunction derives from `bsl&colon;&colon;true&lowbar;type` if (template parameter) `t&lowbar;TYPE` is one of the recognized `bsl&colon;&colon;variant` tag types, and from `bsl&colon;&colon;false&lowbar;type` otherwise&period;

This metafunction requires any cv and ref qualifications to be removed from the queried type&period;

== Base Classes

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

== Specializations

[cols="1,4"]
|===
| Name| Description
| xref:BloombergLP/bslstl/Variant_IsTag-08.adoc[`Variant&lowbar;IsTag&lt;std::allocator&lowbar;arg&lowbar;t&gt;`] 
| This explicit specialization derives from `bsl&colon;&colon;true&lowbar;type` for the `bsl&colon;&colon;allocator&lowbar;arg&lowbar;t` tag type&period;
| xref:BloombergLP/bslstl/Variant_IsTag-0a.adoc[`Variant&lowbar;IsTag&lt;bsl::in&lowbar;place&lowbar;index&lowbar;t&lt;t&lowbar;INDEX&gt;&gt;`] 
| This partial specialization derives from `bsl&colon;&colon;true&lowbar;type` for any specialization of the `bsl&colon;&colon;in&lowbar;place&lowbar;index&lowbar;t` tag type&period;
| xref:BloombergLP/bslstl/Variant_IsTag-07.adoc[`Variant&lowbar;IsTag&lt;bsl::in&lowbar;place&lowbar;type&lowbar;t&lt;t&lowbar;TYPE&gt;&gt;`] 
| This partial specialization derives from `bsl&colon;&colon;true&lowbar;type` for any specialization of the `bsl&colon;&colon;in&lowbar;place&lowbar;type&lowbar;t` tag type&period;
|===



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