[#bsl-enable_if-07]
= xref:bsl.adoc[bsl]::enable_if
:relfileprefix: ../
:mrdocs:

This `struct` template implements the `enable_if` meta‐function defined in the C++11 standard [meta.trans.ptr]. This `struct` template provides a `typedef` `type` that is an alias to the (template parameter) `t_TYPE` if the (template parameter) `t_COND` is `true`; otherwise, `type` is not provided. If `t_TYPE` is not specified, it is set to `void`. Note that this generic default template provides `type` for when `t_COND` is `true`; a template specialization is provided (below) that omits `type` for when `t_COND` is `false`.

== Synopsis

Declared in `<bslmf_enableif.h>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
template<
    bool t_COND,
    class t_TYPE = void>
struct enable_if;
----

== Type Aliases

[cols="1,4"]
|===
| Name| Description
| xref:bsl/enable_if-07/type.adoc[`type`] 
| This `typedef` is an alias to the (template parameter) `t_TYPE`.
|===


== Specializations

[cols="1,4"]
|===
| Name| Description
| xref:bsl/enable_if-0b.adoc[`enable_if<true>`] 
| This `struct` template implements the `enable_if` meta‐function defined in the C++11 standard [meta.trans.ptr]. This `struct` template provides a `typedef` `type` that is an alias to the (template parameter) `t_TYPE` if the (template parameter) `t_COND` is `true`; otherwise, `type` is not provided. If `t_TYPE` is not specified, it is set to `void`. Note that this generic default template provides `type` for when `t_COND` is `true`; a template specialization is provided (below) that omits `type` for when `t_COND` is `false`.
| xref:bsl/enable_if-08.adoc[`enable_if<false, t_TYPE>`] 
| This partial specialization of `enable_if`, for when the (template parameter) `t_COND` is `false`, guarantees that no `typedef` `type` is supplied. Note that this class definition is intentionally empty.
|===



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