[#BloombergLP-bslstl-Variant_AssignsFromType]
= xref:BloombergLP.adoc[BloombergLP]::xref:BloombergLP/bslstl.adoc[bslstl]::Variant_AssignsFromType
:relfileprefix: ../../
:mrdocs:

Determine whether `t_TYPE` assigns to a unique alternative of `t_VARIANT`.

== Synopsis

Declared in `<bslstl_variant.h>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
template<
    class t_VARIANT,
    class t_TYPE>
struct Variant_AssignsFromType
    : xref:bsl/integral_constant-02.adoc[bsl::integral_constant<bool, !bsl::is_same<typename bsl::remove_cvref<t_TYPE>::type, t_VARIANT>::value && Variant_IsAlternativeConstructibleFrom<t_VARIANT, t_TYPE>::value && Variant_isAlternativeAssignableFrom<t_VARIANT, t_TYPE>::value>]
----

== Description

This component‐private metafunction is derived from `bsl::true_type` if (template parameter) `t_TYPE` is neither a tag type nor the type (template parameter) `t_VARIANT` (modulo cv‐qualification), there is a unique best match alternative in `t_VARIANT` for `std::declval<t_TYPE>()`, and that alternative is constructible and assignable from `std::declval<t_TYPE>()`; otherwise, this metafunction is derived from `bsl::false_type`.

This metafunction is used to constrain the converting assignment operator of `bsl::variant`.

== Base Classes

[cols="1,4"]
|===
| Name| Description
| `xref:bsl/integral_constant-02.adoc[bsl::integral_constant<bool, !bsl::is_same<typename bsl::remove_cvref<t_TYPE>::type, t_VARIANT>::value && Variant_IsAlternativeConstructibleFrom<t_VARIANT, t_TYPE>::value && Variant_isAlternativeAssignableFrom<t_VARIANT, t_TYPE>::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`] 
| 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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