Boost C++ Libraries

...one of the most highly regarded and expertly designed C++ library projects in the world. — Herb Sutter and Andrei Alexandrescu, C++ Coding Standards

This is the documentation for a snapshot of the develop branch, built from commit ec9f6e560b.

grammar::variant_rule

Match one of a set of rules.

Synopsis

Defined in header <boost/url/grammar/variant_rule.hpp>

template<
    class... Rules>
constexpr implementation-defined
variant_rule(
    Rules... rn);

Description

Each specified rule is tried in sequence. When the first match occurs, the result is stored and returned in the variant. If no match occurs, an error is returned.

Value Type

using value_type = variant< typename Rules::value_type... >;

Example

Rules are used with the function parse.

// request-target = origin-form
//                / absolute-form
//                / authority-form
//                / asterisk-form

system::result< variant< url_view, url_view, authority_view, core::string_view > > rv = grammar::parse(
    "/index.html?width=full" ,
    variant_rule(
        origin_form_rule,
        absolute_uri_rule,
        authority_rule,
        delim_rule( '*' ) ) );

BNF

variant     = rule1 / rule2 / rule3...

Specification

See Also

absolute_uri_rule, authority_rule, delim_rule, parse, origin_form_rule, url_view.

Convenience header <boost/url/grammar.hpp>