[#BloombergLP-bslstl-Variant_IsAlternativeConstructibleFrom-0e]
= xref:BloombergLP.adoc[BloombergLP]::xref:BloombergLP/bslstl.adoc[bslstl]::Variant_IsAlternativeConstructibleFrom
:relfileprefix: ../../
:mrdocs:

This component‐private metafunction is derived from `bsl::true_type` if there is a unique best match alternative in (template parameter) `t_VARIANT` for 'std::declval<t_TYPE>() and that alternative is constructible from `std::declval<t_TYPE>(), and `bsl::false_type' otherwise.

== Synopsis

Declared in `<bslstl_variant.h>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
template<
    class t_VARIANT,
    class t_TYPE,
    size_t t_INDEX = BloombergLP::bslstl::Variant_ConvertIndex<t_TYPE, t_VARIANT>::value>
struct Variant_IsAlternativeConstructibleFrom
    : xref:bsl/integral_constant-02.adoc[bsl::integral_constant<bool, Variant_IsConstructible<typename bsl::variant_alternative<t_INDEX, t_VARIANT>::type, t_TYPE>::value && Variant_HasUniqueCVType<typename bsl::variant_alternative<BloombergLP::bslstl::Variant_ConvertIndex<t_TYPE, t_VARIANT>::value, t_VARIANT>::type, t_VARIANT>::value>]
----

== Base Classes

[cols="1,4"]
|===
| Name| Description
| `xref:bsl/integral_constant-02.adoc[bsl::integral_constant<bool, Variant_IsConstructible<typename bsl::variant_alternative<t_INDEX, t_VARIANT>::type, t_TYPE>::value && Variant_HasUniqueCVType<typename bsl::variant_alternative<BloombergLP::bslstl::Variant_ConvertIndex<t_TYPE, t_VARIANT>::value, t_VARIANT>::type, t_VARIANT>::value>]`
| 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`] 
| 
|===


== 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 value_type`] 
| 
|===


== Static Data Members

[cols="1"]
|===
| Name
| xref:bsl/integral_constant-02/value.adoc[`value`] 
|===


== Specializations

[cols="1"]
|===
| Name
| xref:BloombergLP/bslstl/Variant_IsAlternativeConstructibleFrom-06.adoc[`Variant_IsAlternativeConstructibleFrom<t_VARIANT, t_TYPE, bsl::variant_npos>`] 
|===



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