= null_visitor

A no-op event visitor that does nothing. Useful as a placeholder or default when
an algorithm requires a visitor but no action is needed, or to fill an unused slot
when combining event visitors.

*Defined in:* `<boost/graph/visitors.hpp>` +
*Models:* xref:visitors/EventVisitor.adoc[EventVisitor]

== Synopsis

[source,cpp]
----
struct null_visitor {
  typedef on_no_event event_filter;

  template <class T, class Graph>
  void operator()(T x, Graph& g);
};
----

== Associated Types

[cols="1,3",options="header"]
|===
| Type | Description

| `event_filter`
| `on_no_event`. The visitor is not associated with any algorithm event.
|===

== Member Functions

[cols="1,3",options="header"]
|===
| Member | Description

| `void operator()(T x, Graph& g)`
| Does nothing.
|===
