[#BloombergLP-bslstl-Variant_TypeToIndexImpl-0a]
= xref:BloombergLP.adoc[BloombergLP]::xref:BloombergLP/bslstl.adoc[bslstl]::Variant_TypeToIndexImpl
:relfileprefix: ../../
:mrdocs:

This component‐private metafunction provides implementation for `Variant_TypeToIndex`. It evaluates to `t_INDEX + i` where `i` is the zero‐based index of (template parameter) `t_TYPE` in (template parameters) `t_HEAD, t_TAIL...`, or `bsl::variant_npos` if `t_TYPE` is not found.

== Synopsis

Declared in `<bslstl_variant.h>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
template<
    size_t t_INDEX,
    class t_TYPE,
    class t_HEAD = BSLSTL_VARIANT_NOT_A_TYPE,
    class... t_TAIL>
struct Variant_TypeToIndexImpl
    : bsl::conditional<bsl::is_same<t_TYPE, t_HEAD>::value, bsl::integral_constant<size_t, t_INDEX>, Variant_TypeToIndexImpl<t_INDEX + 1, t_TYPE, t_TAIL...>>::type
----

== Base Classes

[cols="1,4"]
|===
| Name| Description
| `bsl::conditional<bsl::is_same<t_TYPE, t_HEAD>::value, bsl::integral_constant<size_t, t_INDEX>, Variant_TypeToIndexImpl<t_INDEX + 1, t_TYPE, t_TAIL...>>::type`
| 
|===

== Specializations

[cols="1,4"]
|===
| Name| Description
| xref:BloombergLP/bslstl/Variant_TypeToIndexImpl-07.adoc[`Variant_TypeToIndexImpl<t_INDEX, t_TYPE, BSLSTL_VARIANT_NOT_A_TYPE>`] 
| This partial specialization is used when the list of alternatives `t_HEAD, t_TAIL...` is empty, i.e., `t_TYPE` wasn't found in the originally supplied list of alternatives.
|===


== Derived Classes

[cols="1,4"]
|===
| Name| Description
| xref:BloombergLP/bslstl/Variant_TypeToIndex-00.adoc[`Variant_TypeToIndex<t_TYPE, bsl::variant<t_HEAD, t_TAIL...>>`] 
| 
|===


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