[#BloombergLP-bslstl-Function_InvokerUtilNullCheck-03]
= xref:BloombergLP.adoc[BloombergLP]::xref:BloombergLP/bslstl.adoc[bslstl]::Function_InvokerUtilNullCheck
:relfileprefix: ../../
:mrdocs:

Provides an `isNull` static method that that returns whether or not its argument is "null", i.e., it cannot be invoked. For must `FUNC` types `isNull` always returns `false` as every instance of `FUNC` is invocable. However, specializations of this class, especially for pointer types, have `isNull` functions that sometimes return `true`. This class is a customization point: types outside of this component can (but rarely should) specialize this template. In particular, `bslstl_function` contains a specialization for `bsl::function`.

== Synopsis

Declared in `<bslstl_function_invokerutil.h>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
template<class FUNC>
struct Function_InvokerUtilNullCheck;
----

== Static Member Functions

[cols="1,4"]
|===
| Name| Description
| xref:BloombergLP/bslstl/Function_InvokerUtilNullCheck-03/isNull.adoc[`isNull`] 
| Return `false`.
|===


== Specializations

[cols="1,4"]
|===
| Name| Description
| xref:BloombergLP/bslstl/Function_InvokerUtilNullCheck-09.adoc[`Function_InvokerUtilNullCheck<bsl::function<PROTO>>`] 
| Specialization of null checker for instantiations of `bsl::function`. This specialization treats an empty `bsl::function` as a null object.
| xref:BloombergLP/bslstl/Function_InvokerUtilNullCheck-0a.adoc[`Function_InvokerUtilNullCheck<FUNC*>`] 
| Specialization of dispatcher for pointer objects.
| xref:BloombergLP/bslstl/Function_InvokerUtilNullCheck-07.adoc[`Function_InvokerUtilNullCheck<MEMTYPECLASS::*>`] 
| Specialization of dispatcher for pointer‐to‐member objects.
|===



[.small]#Created with https://www.mrdocs.com[MrDocs]#