:relfileprefix: ../../../
[#34ECF5D7E50506F83CBB36179139274B1E9D1E09]

= Function optional_rule



== Synopsis

Declared in header `</boost/url/grammar/optional_rule.hpp#L96[boost/url/grammar/optional_rule.hpp,window=blank_]>`

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