Boost C++ Libraries

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This is the documentation for a snapshot of the master branch, built from commit 0d4570a792.
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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

result< variant< url_view, url_view, authority_view, 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, variant.

Convenience header <boost/url/grammar.hpp>


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