[#bsl-variant_size-09]
= xref:bsl.adoc[bsl]::xref:bsl/variant_size-07.adoc[variant_size]<xref:bsl/variant.adoc[variant<t_HEAD, t_TAIL...>]>
:relfileprefix: ../
:mrdocs:

Provide the number of alternatives of a `bsl::variant` specialization.

== Synopsis

Declared in `<bslstl_variant.h>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
template<
    class t_HEAD,
    class... t_TAIL>
struct xref:bsl/variant_size-07.adoc[variant_size]<xref:bsl/variant.adoc[variant<t_HEAD, t_TAIL...>]>
    : xref:bsl/integral_constant-02.adoc[bsl::integral_constant<std::size_t, 1 + sizeof...(t_TAIL)>]
    , xref:bsl/integral_constant-02.adoc[bsl::integral_constant<size_t, 1 + sizeof...(t_TAIL)>]
----

== Description

This partial specialization of `variant_size` provides the number of alternatives, `1 + sizeof...(t_TAIL)`, for a `bsl::variant` specialized on (template parameters) `t_HEAD, t_TAIL...`.

== Base Classes

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