[#boost-urls-grammar-ref-0e]
= xref:boost/urls/grammar/ref-0e.adoc[boost::urls::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#L103[boost/url/grammar/parse.hpp]>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
template<xref:boost/urls/grammar/Rule.adoc[Rule] R>
constexpr
/* implementation-defined */
ref(R const& r) noexcept
requires is_rule<R>::value &&
    ! std::is_same<R,
        implementation_defined::rule_ref<R> >::value;
----

== 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.

== Return Value

The rule as a reference type

== Parameters

[cols=2]
|===
| Name
| Description
| *r*
| The rule to use
|===


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