:relfileprefix: ../../../../
[#boost-urls-grammar-optional_rule_t-08friend]

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



== Synopsis

Declared in header `<https://www.github.com/boostorg/url/blob/develop/include/boost/url/grammar/optional_rule.hpp#L76[boost/url/grammar/optional_rule.hpp,window=blank_]>`

[source,cpp,subs="verbatim,macros,-callouts"]
----
template<class R_>
friend
constexpr
xref:boost/urls/grammar/optional_rule_t.adoc[optional_rule_t]<R_>
optional_rule(R_ const& r);
----