:relfileprefix: ../../../
[#boost-urls-grammar-range_rule-05]

== 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#L672[boost/url/grammar/range_rule.hpp,window=blank_]>`

[source,cpp,subs="verbatim,macros,-callouts"]
----
template<
    class Rule1,
    class Rule2>
constexpr
pass:q[_implementation-defined_]
range_rule(
    Rule1 const& first,
    Rule2 const& next,
    std::size_t N = 0,
    std::size_t M = std::size_t(-1)) noexcept;
----

=== 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/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-06.adoc[parse]
.
[,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 ) ) ) );
----
[,cpp]
----
range       = <1>*<1>first
            / first <N-1>*<M-1>next
----

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





=== Parameters

|===
| Name | Description 

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

| *next*
| 
The rule to use for matching
each subsequent 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-02.adoc[delim_rule]
,
xref:boost/urls/grammar/error/end_of_range.adoc[error::end_of_range]
,
xref:boost/urls/grammar/parse-06.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]
.