[#bsl-is_function-05]
= xref:bsl.adoc[bsl]::is_function
:relfileprefix: ../
:mrdocs:

This `struct` template implements the `is_function` meta‐function defined in the C++11 standard [meta.unary.cat]to determine if the (template parameter) `t_TYPE` is a function type. This `struct` derives from `bsl::true_type` if the `t_TYPE` is a function type, and from `bsl::false_type` otherwise. This implementation relies on the fact that neither function types nor reference types can be cv‐qualified so that `is_const<const t_TYPE>` will actually yield `false`.

== Synopsis

Declared in `<bslmf_isfunction.h>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
template<class t_TYPE>
struct is_function
    : xref:bsl/integral_constant-02.adoc[bsl::integral_constant<bool, !is_const<const t_TYPE>::value>]
----

== Base Classes

[cols="1,4"]
|===
| Name| Description
| `xref:bsl/integral_constant-02.adoc[bsl::integral_constant<bool, !is_const<const 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`] 
| 
|===


== 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="1,4"]
|===
| Name| Description
| xref:bsl/is_function-06.adoc[`is_function<t_TYPE&>`] 
| Reference types are, self‐evidently, never function types. The idiom for detecting function types in this component is that a function is a type that is the same as the const‐qualified version of that same type. As references also have this property, we must filter out references with this partial specialization.
| xref:bsl/is_function-01.adoc[`is_function<t_TYPE&&>`] 
| Reference types are, self‐evidently, never function types. The idiom for detecting function types in this component is that a function is a type that is the same as the const‐qualified version of that same type. As references also have this property, we must filter out references with this partial specialization.
|===



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