[#BloombergLP-bdlat_EnumFunctions-HasFallbackEnumerator-00]
= xref:BloombergLP.adoc[BloombergLP]::xref:BloombergLP/bdlat_EnumFunctions.adoc[bdlat_EnumFunctions]::HasFallbackEnumerator
:relfileprefix: ../../
:mrdocs:

Meta‐function that detects whether `TYPE` has a fallback enumerator.

== Synopsis

Declared in `<bdlat_enumfunctions.h>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
template<class TYPE>
struct HasFallbackEnumerator
    : xref:bsl/integral_constant-02.adoc[bsl::integral_constant<bool, bslalg::HasTrait<TYPE, bdlat_TypeTraitHasFallbackEnumerator>::value>]
----

== Description

This `struct` should be specialized for third‐party types that need to declare the fact that they have a fallback enumerator value. Clients that specialize this struct must ensure that if `HasFallbackEnumerator<TYPE>::value` is true, then `IsEnumeration<TYPE>::value` is also true; otherwise, the behavior is undefined.

== Base Classes

[cols="1,4"]
|===
| Name| Description
| `xref:bsl/integral_constant-02.adoc[bsl::integral_constant<bool, bslalg::HasTrait<TYPE, bdlat_TypeTraitHasFallbackEnumerator>::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.
|===


== Specializations

[cols="1,4"]
|===
| Name| Description
| xref:BloombergLP/bdlat_EnumFunctions/HasFallbackEnumerator-01.adoc[`HasFallbackEnumerator<bdlar::EnumConstRef>`] 
| Trait indicating that `bdlar::EnumConstRef` supports a fallback enumerator.
| xref:BloombergLP/bdlat_EnumFunctions/HasFallbackEnumerator-08.adoc[`HasFallbackEnumerator<bdlar::EnumRef>`] 
| Trait indicating that `bdlar::EnumRef` supports a fallback enumerator.
|===



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