:relfileprefix: ../../../
[#boost-urls-grammar-ref-07]

== xref:boost.adoc[pass:[boost]]::xref:boost/urls.adoc[pass:[urls]]::xref:boost/urls/grammar.adoc[pass:[grammar]]::ref


Return a reference to a rule


=== Synopsis

Declared in header `<https://www.github.com/boostorg/url/blob/develop/include/boost/url/grammar/parse.hpp#L131[boost/url/grammar/parse.hpp,window=blank_]>`

[source,cpp,subs="verbatim,macros,-callouts"]
----
template<class Rule>
constexpr
pass:q[_implementation-defined_]
ref(Rule const& r) noexcept;
----

=== Description


This function returns a rule which
references the specified object. This is
used to reduce the number of bytes of
storage (`sizeof`) required by a combinator
when it stores a copy of the object.


Ownership of the object is not transferred;
the caller is responsible for ensuring the
lifetime of the object is extended until it
is no longer referenced. For best results,
`ref` should only be used with compile-time
constants.





=== Parameters

|===
| Name | Description 

| *r*
| 
The rule to use

|===