boost::urls::grammar::range_rule

Match a repeating number of elements

Synopsis

Declared in <boost/url/grammar/range_rule.hpp>

template<
    Rule R1,
    Rule R2>
constexpr
/* implementation-defined */
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 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

using value_type = range< typename Rule::value_type >;

Example

Rules are used with the function parse.

// 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

range       = <1>*<1>first
            / first <N-1>*<M-1>next

Specification

Return Value

A rule that matches the range.

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

alpha_chars, delim_rule, error::end_of_range, parse, range, tuple_rule, squelch.

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