[#BloombergLP-bslstl-Variant_TypeToIndex-00]
= xref:BloombergLP.adoc[BloombergLP]::xref:BloombergLP/bslstl.adoc[bslstl]::xref:BloombergLP/bslstl/Variant_TypeToIndex-0d.adoc[Variant_TypeToIndex]<t_TYPE, xref:bsl/variant.adoc[bsl::variant<t_HEAD, t_TAIL...>]>
:relfileprefix: ../../
:mrdocs:

Compute the zero‐based index of `t_TYPE` in a `bsl::variant`.

== Synopsis

Declared in `<bslstl_variant.h>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
template<
    class t_TYPE,
    class t_HEAD,
    class... t_TAIL>
struct xref:BloombergLP/bslstl/Variant_TypeToIndex-0d.adoc[Variant_TypeToIndex]<t_TYPE, xref:bsl/variant.adoc[bsl::variant<t_HEAD, t_TAIL...>]>
    : xref:BloombergLP/bslstl/Variant_TypeToIndexImpl-0a.adoc[Variant_TypeToIndexImpl<0, t_TYPE, t_HEAD, t_TAIL...>]
----

== Description

This partial specialization of `Variant_TypeToIndex` computes the zero‐based index of `t_TYPE` in the alternatives `t_HEAD, t_TAIL...` of a `bsl::variant` specialization.

== Base Classes

[cols="1,4"]
|===
| Name| Description
| `xref:BloombergLP/bslstl/Variant_TypeToIndexImpl-0a.adoc[Variant_TypeToIndexImpl<0, t_TYPE, t_HEAD, t_TAIL...>]`
| Compute `t_INDEX + i` where `i` is the index of `t_TYPE`, or `npos`.
|===


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