:relfileprefix: ../../../
[#CC140B4C18D2616EFD643FC4A88449C611695CC4]

= Function optional_rule



== Synopsis

Declared in header `</boost/url/grammar/optional_rule.hpp#L77[boost/url/grammar/optional_rule.hpp,window=blank_]>`

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

