:relfileprefix: ../../../
[#boost-urls-grammar-range_rule-00]

== xref:boost.adoc[pass:[boost]]::xref:boost/urls.adoc[pass:[urls]]::xref:boost/urls/grammar.adoc[pass:[grammar]]::range_rule


Match a repeating number of elements


=== Synopsis

Declared in header `<https://www.github.com/boostorg/url/blob/develop/include/boost/url/grammar/range_rule.hpp#L458[boost/url/grammar/range_rule.hpp,window=blank_]>`

[source,cpp,subs="verbatim,macros,-callouts"]
----
template<class Rule>
constexpr
pass:q[_implementation-defined_]
range_rule(
    Rule const& next,
    std::size_t N = 0,
    std::size_t M = std::size_t(-1)) noexcept;
----

=== Description


Elements are matched using the passed rule.


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

=== Rules are used with the function

xref:boost/urls/grammar/parse-02.adoc[parse]
.
[,cpp]
----
// range    = 1*( ";" token )

system::result< range<core::string_view> > rv = parse( ";alpha;xray;charlie",
    range_rule(
        tuple_rule(
            squelch( delim_rule( ';' ) ),
            token_rule( alpha_chars ) ),
        1 ) );
----
[,cpp]
----
range        = <N>*<M>next
----

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





=== Parameters

|===
| Name | Description 

| *next*
| 
The rule to use for matching
each element. The range extends until this
rule returns an error.

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

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

|===




=== See Also


xref:boost/urls/grammar/alpha_chars.adoc[alpha_chars]
,
xref:boost/urls/grammar/delim_rule-0a.adoc[delim_rule]
,
xref:boost/urls/grammar/error/end_of_range.adoc[error::end_of_range]
,
xref:boost/urls/grammar/parse-02.adoc[parse]
,
xref:boost/urls/grammar/range.adoc[range]
,
xref:boost/urls/grammar/tuple_rule.adoc[tuple_rule]
,
xref:boost/urls/grammar/squelch.adoc[squelch]
.