[#boost-urls-grammar-range_rule-06]
= xref:boost.adoc[boost]::xref:boost/urls.adoc[urls]::xref:boost/urls/grammar.adoc[grammar]::range_rule
:relfileprefix: ../../../
:mrdocs:


Match a repeating number of elements

== Synopsis


Declared in `<https://www.github.com/boostorg/url/blob/develop/include/boost/url/grammar/range_rule.hpp#L509[boost/url/grammar/range_rule.hpp]>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
template<
    xref:boost/urls/grammar/Rule.adoc[Rule] R1,
    xref:boost/urls/grammar/Rule.adoc[Rule] R2>
constexpr
/* implementation-defined */::xref:boost/urls/grammar/implementation_defined/range_rule_t.adoc[range_rule_t]<R1, R2>
range_rule(
    R1 const& first,
    R2 const& next,
    std::size_t N = 0,
    std::size_t M = std::size_t(‐1)) noexcept
requires ! std::is_integral<R2>::value;
----

== Description


Two rules are used for match. The rule    `first` is used for matching the first    element, while the `next` rule is used    to match every subsequent element.        Normally when the rule returns an error,    the range ends and the input is rewound to    one past the last character that matched    successfully. However, if the rule returns    the special value xref:boost/urls/grammar/error.adoc[error::end_of_range], the    input is not rewound. This allows for rules    which consume input without producing    elements in the range. For example, to    relax the grammar for a comma‐delimited    list by allowing extra commas in between    elements.


=== Value Type

[,cpp]
----
using value_type = range< typename Rule::value_type >;
----

=== Example

Rules are used with the function xref:boost/urls/grammar/parse-02.adoc[parse]&period;

[,cpp]
----
// range    = [ token ] *( "," token )

system::result< range< core::string_view > > rv = parse( "whiskey,tango,foxtrot",
    range_rule(
        token_rule( alpha_chars ),          // first
        tuple_rule(                      // next
            squelch( delim_rule(',') ),
            token_rule( alpha_chars ) ) ) );
----

=== BNF

[,cpp]
----
range       = <1>*<1>first
            / first <N-1>*<M-1>next
----

=== Specification

* link:https://datatracker.ietf.org/doc/html/rfc5234#section-3.6[3&period;6&period;  Variable Repetition (rfc5234)]



== Parameters


|===
| Name | Description

| *first*
| The rule to use for matching    the first element&period; If this rule returns    an error, the range is empty&period;


| *next*
| The rule to use for matching    each subsequent element&period; The range extends    until this rule returns an error&period;


| *N*
| The minimum number of elements for    the range to be valid&period; If omitted, this    defaults to zero&period;


| *M*
| The maximum number of elements for    the range to be valid&period; If omitted, this    defaults to unlimited&period;


|===

== See Also


xref:boost/urls/grammar/alpha_chars.adoc[alpha&lowbar;chars],        xref:boost/urls/grammar/delim_rule-01.adoc[delim&lowbar;rule],        xref:boost/urls/grammar/error.adoc[error&colon;&colon;end&lowbar;of&lowbar;range],        xref:boost/urls/grammar/parse-02.adoc[parse],        xref:boost/urls/grammar/range.adoc[range],        xref:boost/urls/grammar/tuple_rule.adoc[tuple&lowbar;rule],        xref:boost/urls/grammar/squelch.adoc[squelch]&period;






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