[#boost-urls-grammar-ref-0e]
= xref:boost.adoc[boost]::xref:boost/urls.adoc[urls]::xref:boost/urls/grammar.adoc[grammar]::ref
:relfileprefix: ../../../
:mrdocs:


Return a reference to a rule

== Synopsis


Declared in `<https://www.github.com/boostorg/url/blob/develop/include/boost/url/grammar/parse.hpp#L102[boost/url/grammar/parse.hpp]>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
template<xref:boost/urls/grammar/Rule.adoc[Rule] R>
constexpr
/* implementation-defined */::xref:boost/urls/grammar/implementation_defined/rule_ref.adoc[rule_ref]<R>
ref(R 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


|===



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